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FEBRUARY 1994
DS3605-2.2
GP1020
SIX-CHANNEL PARALLEL CORRELATOR CIRCUIT FOR GPS OR GLONASS RECEIVERS
The GP1020 is a six-channel CMOS digital correlator which has been designed to work with the GP1010 L1-channel downconverter or other integrated circuits, and may be used to acquire and track the GPS C/A code or the GLONASS signals. For each of the six channels the GP1020 includes independent digital down-conversion to baseband, C/A code generation, correlation, and accumulate-and-dump registers. The GP1020 interfaces with a microprocessor via a 16-bit data bus to control the acquisition and tracking processes using the various registers on the chip.
90
61
91
60
FEATURES
GP1020
s Six Fully Independent Correlation Channels s Switchable to Receive GPS or GLONASS Codes s Input Multiplexer for Multiple GPS Front-Ends - Allows
Antenna Diversity
120
31
s Input Multiplexer for GLONASS Multiple (Separate
Channels) Front-Ends
s Digital Interface Compatible with Most 16 or 32-Bit
Microprocessors
1
30
GP120
Fig 1 Pin connections - top view
s Fully Compatible with GP1010 GPS Receiver Front-End s Sideways Stackable to give Multiples of Six Channels s 120-pin Plastic Quad Flatpack s Power Dissipation Less Than 500mW
APPLICATIONS
ABSOLUTE MAXIMUM RATINGS
These are not the operating conditions, but are the absolute limits which if exceeded, even momentarily, may cause permanent damage. To ensure sustained correct operation the device should be used within the limits given under Electrical Characteristics. Supply voltage (VDD) from ground (VSS): 20*3V to16*0 V Input voltage (any input pin): VSS20*3V to VDD10*3 V Output voltage (any output pin): VSS20*3V to VDD10*3 V Storage temperature: 255C to 1125C
s GPS or GLONASS Navigation Systems s High Integrity Combined Receivers s GPS Geodetic Receivers s GPS Time Reference
ORDERING INFORMATION
The GP1020 is available in 120-pin Quad Flatpacks (Gullwing formed leads) in both Commercial (0C to 170C) and Industrial (240C to 185C) grades. The ordering codes below are for standard screened devices.
RELATED PRODUCTS
Part Description Datasheet Reference DS3861 DS3076
ORDERING CODES
GP1020 CG GPKR Commercial - Plastic 120-pin QFP (GP120) GP1020 IG GPKR Industrial - Plastic 120-pin QFP (GP120)
DW9255 35*42MHz SAW Filter GP1010 GPS Receiver Front-End
GP1020
TYPICAL GPS RECEIVER (Fig. 2)
All satellites use the same L1 frequency of 1575*42MHz, but different Gold codes, so a single front-end may be used. To achieve better sky coverage it may be desirable to use more than one antenna, in which case separate front-ends will be needed.
GND MASTER CLK SAMPLE CLK SIGN MAG VSS 15V VDD MASTERRESET NAVIGATION SOLUTION
GP1010 & FILTER
MASTER/SLAVE
CS
DECODE DATA BUS (16) ADDR BUS (8) CONTROL
SIGN 0 MAG 0 SIGN 1 MAG 1
GP1020 (MASTER)
TIC OUT INT OUT
MICROPROCESSOR SYSTEM
3
MULTIPLE ANTENNAS TO GIVE WIDER SKY COVERAGE
SLAVECLK
TIC IN SIGN 0 MAG 0 SIGN 1 MAG 1 INT IN
OPTIONAL SECOND GP1010 & FILTER
CS
DECODE
OPTIONAL SECOND GP1020 (SLAVE)
VSS
VDD MASTER/SLAVE
15V
GND
MASTERRESET
Fig. 2 GPS receiver simplified block diagram
TYPICAL GLONASS RECEIVER (Fig. 3)
Each satellite will use a different `L1' carrier frequency, in the range 1602*5625 to 1615*500MHz, with 0*5625MHz spacing, but all with the same 511-bit spreading code. The normal method for receiving these signals is to use several front-ends, perhaps with the first LNA and mixer common, but certainly with different final local oscillators and mixers.
GLONASS FRONT-END FILTERS, AMPLIFIERS AND MIXERS
CHANNEL SELECTION AND ADC CHANNEL SELECTION AND ADC CHANNEL SELECTION AND ADC CHANNEL SELECTION AND ADC CHANNEL SELECTION AND ADC FREQUENCY GENERATOR CHANNEL SELECTION AND ADC SAMPLE CLK SIGN MAG SIGN MAG SIGN MAG SIGN MAG SIGN MAG SIGN MAG
GND VSS
15V VDD
MASTER/SLAVE
L-BAND DOWN CONVERTER
SAMP CLK SIGN 0 MAG 0 SIGN 1 MAG 1 SIGN 2 MAG 2 SIGN 3 MAG 3 SIGN 4 MAG 4 SIGN 5 MAG 5
NAVIGATION SOLUTION MASTERRESET
CS
DECODE
MICROPROCESSOR SYSTEM
DATA BUS (16)
GP1020
ADDR BUS (8) CONTROL 3 INT OUT
MASTER CLOCK
OSCILLATOR FREQUENCY SELECTION
Fig. 3 GLONASS receiver simplified block diagram
2
GP1020
PIN DESCRIPTIONS (See Application Notes, p. 41)
All VSS and all VDD pins must be used in order to ensure reliable operation. Several pins, such as Satellite Inputs 2 to 9 Sign and Magnitudes are also used for device testing, but only as a secondary function. Pin No.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Pin No.
66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120
Signal name
TICIN TICOUT D0 D1 VSS VDD D2 D3 TIME MARK RTCINT MARKFB1 MARKFB2 D4 D5 VDD VSS D6 D7 WPROG NANDA NANDB TDO TCK TRST NANDOP TMS TDI MARKFB3 TDO7 DISCOP TDO6 TDO5 D8 D9 VSS VDD D10 D11 TDO4 TDO3 TDO2 TDO1 D12 D13 VDD VSS D14 D15 ALE A1 A2 A3 A4 A5 A6
Type
I O I/O I/O 2 1 I/O I/O O I I I I/O I/O 1 2 I/O I/O I I I O I I O I I I O O O O I/O I/O 2 1 I/O I/O O O O O I/O I/O 1 2 I/O I/O I I I I I I I
Description
TIC input to slave TIC output from Master Data Bus, bit 0 Data Bus, bit 1 Ground Positive supply Data Bus, bit 2 Data Bus, bit 3 One pulse per second output Real time clock interrupt input Timemark line driver feedback Timemark line driver feedback Data Bus, bit 4 Data Bus, bit 5 Positive supply Ground Data Bus, bit 6 Data Bus, bit 7 Bus timing mode - see note 2 Test Structure - see note 3 Test Structure - see note 3 Boundary Scan output Boundary Scan clock Boundary Scan reset Test Structure - see note 3 Boundary Scan control Boundary Scan input Timemark line driver feedback Serial Test Data Output 7 On/Off control for LNA by GP1010 Serial Test Data Output 6 Serial Test Data Output 5 Data Bus, bit 8 Data Bus, bit 9 Ground Positive supply Data Bus, bit 10 Data Bus, bit 11 Serial Test Data Output 4 Serial Test Data Output 3 Serial Test Data Output 2 Serial Test Data Output 1 Data Bus, bit 12 Data Bus, bit 13 Positive supply Ground Data Bus, bit 14 Data Bus, bit 15 Address Latch Enable, bus control Register Address, bit 1 (LSB) Register Address, bit 2 Register Address, bit 3 Register Address, bit 4 Register Address, bit 5 Register Address, bit 6
Signal name
A7 A8 MASTER/ SLAVE TSCAN TCKS TDI1 MASTER RESET MOT/INTEL CS VSS VDD WEN RW TMS2 TMS1 TMAG TSIGN MAG2 100/219kHz VDD VSS INTOUT SIGN2 MAG3 SIGN3 MAG4 SIGN4 MAG5 SIGN5 MAG6 SIGN6 MAG7 SIGN7 MAG8 SIGN8 MAG9 SIGN9 MAG1 SIGN1 VSS VDD MAG0 SIGN0 SAMPCLK VDD MASTERCLK VSS Bias VSS VDD VSS CLKSEL PLLLOCKIN BITECNTL GLONASSBIT SLAVECLK INTIN TCK1 TCK2 TCK3 TCK4 TCK5 TCK6 TCK7 TCK8
Type
I I I I I I I I I 2 1 I I I I O O I/O O 1 2 O I/O I/O I/O I/O I/O I/O I/O I/O I/O I/O I/O I/O I/O I/O I/O I/O I/O 2 1 I I O 1 I 2 O 2 1 2 I I O I I/O I I/O I/O I/O I/O I/O I/O I/O I
Description
Register Address, bit 7 Register Address, bit 8 Master or slave mode select Scan Test mode select Test Clock select Serial Test Data Input Master Reset (active low) Motorola (hi) or Intel (lo) bus select Chip Select (active low) for bus Ground Positive supply Bus control - see note 1 Bus control - see note 1 Test Mode Select 2 Test Mode Select 1 Test PRN Pattern Magnitude o/p Test PRN Pattern Sign output Satellite Input 2, Magnitude Programmable Interrupt Timer clock Positive supply Ground Interrupt out to microprocessor Satellite Input 2, Sign Satellite Input 3, Magnitude Satellite Input 3, Sign Satellite Input 4, Magnitude Satellite Input 4, Sign Satellite Input 5, Magnitude Satellite Input 5, Sign Satellite Input 6, Magnitude Satellite Input 6, Sign Satellite Input 7, Magnitude Satellite Input 7, Sign Satellite Input 8, Magnitude Satellite Input 8, Sign Satellite Input 9, Magnitude Satellite Input 9, Sign Satellite Input 1, Magnitude Satellite Input 1, Sign Ground Positive supply Satellite Input 0, Magnitude Satellite Input 0, Sign Sampling clock to down-converter Positive supply 40MHz Master Clock Ground Bias for MASTERCLK in 600mV AC-coupled mode Ground Positive supply Ground Sets 100/219kHz to 100or 219kHz PLL lock status from down-converter BITE control to down-converter I/P to monitor GLONASS front-end 20MHz clock from Master to slave Interrupt to slave to sync to Master Test Clock 1 Test Clock 2 Test Clock 3 Test Clock 4 Test Clock 5 Test Clock 6 Test Clock 7 Test Clock 8
NOTE 1. The functions of RW and WEN pins depend on whether the GP1020 is in MotorolaTM (MOT/INTEL = `1') or IntelTM mode (MOT/INTEL = `0'). In Motorola mode, WEN is an enable (active high) and RW is Read/ Write select (`1' = Read). In Intel mode RW is Read, active low, and WEN is Write, also active low.
MOT/INTEL 1 1 0 0
Mode Motorola Motorola Intel Intel
WEN 1 1 1 0
RW 0 1 0 1
Function Write Read Read Write
NOTE 2. WPROG is used to modify the timing of bus operations; when it is held HIGH the internal write signal is ORed with ALE to allow time for the internal address lines to stabilise; when it is held LOW there is no delay added to write. NOTE 3. NANDOP (pin 90) is the output of a spare gate with inputs on NANDA (pin 85) and NANDB (pin 86).
3
GP1020
ELECTRICAL CHARACTERISTICS
These characteristics are guaranteed over the following conditions (unless otherwise stated): Supply voltage, VDD = 5V 10%; Ambient Temperature, TAMB = 0C to 170C (CG grade),240C to 185C (IG grade). DC CHARACTERISTICS Characteristic Min. Supply current, IDD, chip fully active CMOS inputs with pullup resistors to VDD : RTCINT, MASTER/SLAVE, MARKFB (3:1), NANDA, NANDB, WPROG, ALE Input voltage high Input voltage low Pullup resistor CMOS inputs with pulldown resistors to VSS : MOT/INTEL, CLKSEL, INT IN, TIC IN Input voltage high Input voltage low Pulldown resistor CMOS inputs without either pullup or pulldown resistors: MASTERRESET, CS, WEN, RW, MASTERCLK (note 1), SLAVECLK, A (8:1), D (15:0), TCK, TDI, TMS, TRST Input voltage high Input voltage low Input leakage current TTL inputs with pullup resistors to VDD : SIGN (9:0), MAG (9:0), PLLLOCKIN, GLONASSBIT Input voltage high Input voltage low Pullup resistor TTL inputs with pulldown resistors to VSS : TSCAN, TCKS, TDI1, TMS1, TMS2 Input voltage high Input voltage low Pulldown resistor Input for low level clocks: MASTERCLK (note 1) Peak to peak sinewave Power level 1 outputs: TMAG, TSIGN, TDO, TDO (7:1), NANDOP Output voltage high Output voltage low Power level 3 outputs: 100/219kHz, INT OUT, SAMPCLK, TIC OUT, BITE CNTL, DISCOP, TIMEMARK Output voltage high Output voltage low Power level 1 outputs with tri-state: MAG (9:2), SIGN (8:2), TCK (7:1) Output voltage high Output voltage low Output leakage current Power level 3 output with tri-state: SLAVECLK Output voltage high Output voltage low Output leakage current Power level 6 output with tri-state: D (15:0) Output voltage high Output voltage low Output leakage current Bias output: BIAS
NOTE 1.
Value Typ. Max. 100
Units mA
Conditions
0*8VDD 20 75 0*2VDD 250
V V k
0*8VDD 20 75 0*2VDD 250
V V k
0*8VDD 1 0*2VDD 10
V V A
VSS2*0 20 75 0*8 250
V V k
2*0 20 600 VDD21 VDD20*5 0*2 75 0*8 250
V V k mV V V AC coupled IOH = 21*5mA IOL = 1*5mA IOH = 24*5mA IOL = 4*5mA
0*4
VDD21
VDD20*5 0*2
0*4
V V
VDD21
VDD20*5 0*2 VDD20*5 0*2 VDD20*5 0*2
0*4 10 0*4 10 0*4 10
V V A V V A V V A
IOH = 21*5mA IOL = 1*5mA VSSVDD21
VDD21
Special output to be used only as shown in Fig. 12 (page 8)
The input MASTERCLK may be driven by either CMOS logic levels or by a low amplitude sinewave if the BIAS pin is connected as shown in Fig. 12.
4
GP1020
TIMING CHARACTERISTICS (See Figs. 4 to 9) Characteristic Symbol Value Min. Address hold time ALE pulse width ALE valid to WEN or RW valid (WPROG = 1) ALE valid to WEN or RW valid (WPROG = 0) Address valid to ALE low Address valid to WEN or RW valid CS high to ALE valid CS low to WEN or RW valid Data hold time Data setup time RW high to data at high impedance RW valid to data valid RW valid to WEN high WEN low to RW not valid Write pulse width CS hold time after RW or WEN not valid tAHOLD tALEPW tALESETUP tALVWRV tASETUP tAVWRV tCHALV tCVWRV tDHOLD tDSETUP tRHDZ tRVDV tRWVWENH tWENLRWNV tWLWH tWRCH 10 20 5 20 20 20 10 0 10 30 10 10 15 15 30 0 Max. ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns Units Conditions
25 50
NOTE. This timing information is based on simulations and is not verified by measurement on each device.
GP1020 BUS TIMING DIAGRAMS
WEN tCVWRV CS tALESETUP tWLWH ALE tALEPW tASETUP A (8:1) tAHOLD A (8:1) tDSETUP D (15:0) RW (HIGH) tDHOLD D (15:0) WEN (HIGH) tCHALV
NEXT R/W
RW tWRHCH CS tALESETUP ALE tALEPW tASETUP tAHOLD tCHALV
NEXT R/W
tCVWRV
tWRHCH
ADDRESS VALID
ADDRESS VALID
tRVDV
DATA VALID
tRHDZ
DATA VALID
Fig. 4 Intel 486 mode WRITE. MOT/INTEL = 0, WPROG = 1 (Write inhibited until ALE falling edge)
WEN tCVWRV CS tALVWRV ALE tAVWRV A (8:1) tAHOLD
ADDRESS VALID
Fig. 5 Intel 486 mode READ. MOT/INTEL = 0, WPROG = 1
RW
tWRHCH tWLWH
CS
tCVWRV
tWRHCH
tCHALV
NEXT R/W
tALVWRV ALE tAVWRV A (8:1) tAHOLD
ADDRESS VALID
tCHALV
NEXT R/W
tDSETUP D (15:0) RW (HIGH)
tDHOLD
D (15:0) WEN (HIGH)
tRVDV
DATA VALID
tRHDZ
DATA VALID
Fig. 6 Intel 186 mode WRITE. MOT/INTEL = 0, WPROG = 0
Fig. 7 Intel 186 mode READ. MOT/INTEL = 0, WPROG = 0
5
GP1020
GP1020 BUS TIMING DIAGRAMS (continued)
WEN tCVWRV CS tALVWRV ALE tAVWRV A (8:1) tAHOLD
ADDRESS VALID
WEN
tWRHCH tWLWH
tCVWRV CS
tWRHCH
tCHALV
NEXT R/W
tALVWRV ALE tAVWRV A (8:1) tAHOLD
ADDRESS VALID
tCHALV
NEXT R/W
tDSETUP D (15:0) tRWVWENH RW
tDHOLD
tRVDV D (15:0) tRWVWENH RW
DATA VALID
tRHDZ
DATA VALID
tWENLRWNV
tWENLRWNV
Fig. 8 Motorola 68xxx mode WRITE. MOT/INTEL = 1, WPROG = 0
Fig. 9 Motorola 68xxx mode READ. MOT/INTEL = 1, WPROG = 0
SIGNAL PROCESSING OVERVIEW
Each channel of the GP1020 is fed with a 2-bit (or optionally with a 1-bit) GPS digital IF at around 1*4MHz, from the input multiplexer that connects one of ten signal sources to the channel input. This signal is first brought to baseband using an on-chip digital mixer driven by a programmable digital local oscillator. It is then correlated with a C/A code internally generated by a programmable Gold code generator; the correlation result is the sum of the comparisons of individual code chips over a complete code period (an `epoch' in GPS terminology). A large positive or a large negative sum indicate good correlation but with opposite modulation, where the size of `large' will depend on the current signal to noise ratio, while a small sum indicates poor correlation and the need to adjust the loops or choose another satellite. These results form the `Accumulated Data' and are made available to the microprocessor to both control the tracking loops and to give the broadcast satellite data, the `Navigation Message' when demodulated. Periodically, the code epoch count, the code phase, and the carrier phase of all channels, are sampled at the same instant to form the `Measurement Data' and are also made available to the processor. TIMEBASE GENERATOR The Time Base Generator produces, among other signals: a 505*05 s free-running interrupt timebase INT OUT, a freerunning TIC OUT signal with a period which may be selected to be either 100ms or 9*09ms (approximately), and a TIME MARK signal with a 1 second period as an output which may be locked to GPS time, UTC, or the receiver timebase by programming its delay relative to the TIC, based on recent navigation solutions. The TIC is mainly used to latch measurement data (epoch count, code phase, code DCO phase and integrated carrier phase ( = DCO phase and cycle count)) of all six channels at the same instant. BITE INTERFACE The Bite Interface block contains a register which allows control over the built-in-test functions of the chip. In addition, this register allows the processor to read the state of discrete input pins, such as PLLLOCKIN connected to the status output of the GP1010, and also to set the state of the BITE CNTL and the DISCOP output pins. These can in turn, for example, be used to drive the GP1010 BITE input pin and the LNA power on/off select, respectively. STATUS REGISTERS The Status Registers block contains registers describing the status of accumulated and measurement data provided by each channel. SIGNAL SELECTION BLOCK The Signal Selection block contains a multiplexer which can be programmed to direct any of the ten input sources to any of the six tracking channels. This is needed in GLONASS where frequency division multiplexing is used and separate local oscillators are needed to receive each satellite, leading to separate IF filter channels. An input selector may be desirable in GPS, which uses code division multiplexing, to allow the use of multiple antennae to overcome problems of incomplete sky visibility. For SIGN inputs, LOW = 2, HIGH = 1; for MAG inputs, LOW = 1, HIGH = 3.
DESCRIPTION OF BLOCKS (see Fig. 10)
CLOCK GENERATOR The Clock Generator block generates the various clocks required in the GP1020, which can be operated either as a master or as a slave device. When it is operated as a master, the Clock Generator block is driven by a 40MHz clock provided by the accompanying front-end chip, the GP1010, and to drive the slaves a 20MHz output SLAVE CLK is provided. When the GP1020 is operated as a slave, it is driven only by this 20MHz SLAVE CLK from the master device. In the master the 40MHz is divided in a counter to form seven clock phases to control the data flow, but to get the same timing in the slaves twin 20MHz dividers use both high and low phases separately to give the effect of 40MHz clocking. When in master mode these seven phases are also used to generate a sampling clock (SAMP CLK) output at 40MHz47 = 5*71MHz, which drives the data sampling clock input of the GP1010. A 100/219kHz output is provided for use as a microprocessor Programmable Interrupt Clock.
TRACKING MODULE BLOCKS
The six Tracking Module blocks are all identical so that the term CHx is used in the description to mean any of CH1, CH2,
6
GP1020
SIGN & 2 MAG MASTER CLK SLAVE CLK SAMP CLK MASTER/SLAVE CLOCK GENERATOR 2 INPUT SELECTOR (DUAL 11 TO 7 MUX) CLOCKS TRACKING MODULE CHANNEL 1 TRACKING MODULE CHANNEL 2 TRACKING MODULE CHANNEL 3 TRACKING MODULE CHANNEL 4 TRACKING MODULE CHANNEL 5 TRACKING MODULE CHANNEL 6 TEST SIGN & MAG
8 7 8 7 BITE INTERFACE SELF TEST GENERATOR
10 SETS OF SIGN & MAG INPUT SIGNALS

7 STATUS REGISTER 7 MICROPROCESSOR BUS 7 STATISTICS CHECK
TIC IN INT IN INT OUT TIC OUT TIMEMARK
TIMEBASE GENERATOR
TIC
7
Fig. 10 Simplified overall block diagram
CH3, CH4, CH5 or CH6 inputs or registers. They have the architecture shown in Fig. 11. The individual sub-blocks are as follows: CARRIER DCO The Carrier DCO is an accumulator performing additions at a constant rate and with a programmable increment value. It is used to synthesise the digital local oscillator signal required to bring the input signal to baseband in the mixer block, and must be adjusted away from nominal to allow for Doppler shift and crystal frequency error. The nominal frequency of the output is 1*405396825 MHz, set by loading the 26 bit CHx_CARR_INCR register to 01F7B1B9H and is programmed with a resolution of 42*57475 milliHertz. The very fine resolution is needed to keep the DCO in phase with the satellite signal. CODE DCO This block is a similar structure to the Carrier DCO block and is used to synthesise the oscillator signal required to drive the code generator at the proper chipping rate and phase. The nominal frequency of the output is 2*046MHz, to give a chip rate of 1*023MHz, and is set by loading the 25 bit CHx_CODE_INCR register to 016EA4A8H and is programmed with a resolution of 85*14949 milliHertz. Again,the very fine resolution is needed to keep the DCO in phase with the satellite signal. CODE GENERATOR This generates the processor-selected GPS Gold code (one of PRN code numbers 1 to 32 for normal satellites or 33 to 37 for ground based use) or the GLONASS code (fixed for all satellites) or one of eight INMARSAT codes. Twin generators are used to produce both a prompt (on-time) pattern and an early, late, or early-minus-late version for tracking use. At the end of each code sequence a signal DUMP is generated to latch the Accumulated Data, separately for each channel. MIXER AND CORRELATOR The Mixer and Correlator first mixes the digitised input signal with the Carrier DCO digital local oscillator to generate a signal at baseband, and then uses the Code Generator outputs to correlate the data stream. The block includes in-phase and phase-quadrature channels, as well as prompt and dithered (or early/late) correlator arms. The term dither is used in the GP1020 to mean a code channel in which the timing alternates one half-chip either before or after the prompt channel, and not the now obsolete technique of Taudither, in which the prompt arm timing is oscillated a little each side of nominal to give tracking with only one arm. QUADRUPLE INTEGRATE AND DUMP The bit-by-bit results from the correlator are passed to the Quadruple Integrate And Dump block, which integrates the correlation result of individual code chips from all four correlators (in-phase and phase-quadrature, prompt and dithered arms) over a complete code period. Through the Accumulated Data registers, the processor has access to each integration result.
NAVIGATION OR TIME REFERENCE RECEIVER HARDWARE SYSTEM DESIGN
A receiver system can use one or more GP1020s. When only one is used, that IC is operated in master mode, and when more than one are used, one of them is designated as being the master and all of the others are operated as slaves. In all cases, the master chip is the one which will receive the 40MHz MASTER CLK from the GP1010 and generate, upon release of the MASTERRESET signal, a gated 20MHz clock which drives all slaves (if any) and allows a synchronised start-up. The master device also generates the SAMP CLK signal which drives all of the GP1010 front-ends. The operating mode is programmed by tying the MASTER/ SLAVE pin to VDD for master or to VSS for slave operation. The operating mode sets the functions of MASTER CLK, SLAVE CLK and SAMP CLK pins. The TIME MARK signal is generated by the master GP1020; the slave TIME MARK generator, although not disabled, is not synchronised with the master. The TIC signal is generated by the master and routed to the slaves to ensure a common measurement data sampling instant for all the tracking channels. The slave TIC OUT signal is not disabled but is not used. The master INT OUT drives the slaves' INT IN pins to provide latching of status bits at a common instant. Optionally, the slave TIC OUT and INT OUT pins could be connected to the master TIC IN and INT IN pins, respectively, for testing purposes. When more than one GP1020 is used in the same system, the devices must share a common TIC for sampling of measurement data to enable the software to calculate clock bias in the pseudoranges, and so find the correct ranges. Each GP1020 contains a state machine driven by 7 different clock phases, so for two GP1020s to share a common TIC, the devices must be synchronised. This is achieved by configuring the hardware as follows:
* *
All GP1020s share the same MASTERRESET signal. One GP1020 is designated the master chip. It is
7
GP1020
Q_EOL 4 14-BIT ACCUMULATE AND DUMP Q_PROMPT 4 INPUT SIGN & MAG 4*3MHz IF SAMPLED AT5*7MHz 2 TO GIVE 1*4MHz INTO GP1020 (VIA INPUT SELECTOR) QUADRATURE BASEBAND Cos (vt) 1*4MHz 3 1 PROMPT C/A EOL C/A CODE GENERATOR CODE DCO EPOCH COUNTERS 4 14-BIT ACCUMULATE AND DUMP
MICROPROCESSOR BUS
CARRIER DCO Sin (vt) 1*4MHz
CARRIER CYCLE COUNTER
CLOCK TIC 3 4
CLOCK TIC I_PROMPT 4
CLOCK TIC
CLOCK TIC
IN-PHASE BASEBAND
14-BIT ACCUMULATE AND DUMP I_EOL 4 14-BIT ACCUMULATE AND DUMP
Fig. 11 Tracking module simplified block diagram
programmed into this mode by tying the MASTER/SLAVE pin to VDD (or by leaving it unconnected and relying on an internal pull-up resistor.) All other GP1020s are designated slaves and are programmed into this mode by tying their MASTER/ SLAVE pin to VSS. The master GP1020's SAMP CLK output drives all of the GP1010 front-ends. This ensures that in a multiple GP1010 application, all of the signals are being sampled at the same instant in all GP1010s. The slave GP1020s have their SAMPLING CLK output left unconnected. The SLAVE CLK output from the master drives the SLAVE CLK inputs on all slaves.
* * *
GP1020 INTERNAL CIRCUIT 1-10n MASTER CLK 600mV FROM GP1010 1k 5k BIAS
10n
When the MASTERRESET is released, the clock generators of all devices - master and slaves - are enabled. The SLAVE CLK output of the master device will start to toggle only after the master's clock generator has reached a certain phase (200ns after the MASTERRESET release). The clock generator of the slave device gets reset into a state which corresponds to the next phase and starts counting as soon as the SLAVE CLK signal from the master reaches its SLAVE CLK input pin.
Fig. 12 Biasing circuit for master clock
SAMP CLK 40MHz47 = 5*7142857MHz output when the chip is in master mode; nominal mark:space ratio is 1:1. This signal is held low during an active MASTERRESET and when in slave mode. TICOUT Output signal from TIC generator, used to sample measurement data and so initiate a navigation solution. TIC does not drive the microprocessor directly but sets a flag in MEAS_STATUS_A , which should be be examined by reading the register periodically, such as at every INT OUT. TIC OUT is active high; active time duration is either 4*54545ms for a short TIC or 9*0909ms for a long TIC. The rising edge of TIC OUT is in advance of the effective sampling instant inside the device by 125ns. The TIC period is selectable via the TIC_PERIOD bit of TIMER_CNTL register to either 100ms minus 100ns (= 99*9999ms) or to 9.0909 ms. TIC IN The TIC IN input of a GP1020 is normally provided by a companion GP1020. Its use is controlled by the TIC_SOURCE bit of the TIMER_CNTL register and is configured in most applications so the master TIC OUT drives the slave TIC IN.
IMPORTANT TIMING SIGNALS IN A TYPICAL HARDWARE DESIGN
MASTER CLK The MASTER CLK is a 40MHz clock which sets the timing of all functions in a GPS receiver using the GP1020. In a multiple GP1020 system only the master is given this clock and this may be connected in either of two ways, depending on the signal level. If the clock is a TTL signal it is directly connected to the MASTER CLK input and the BIAS output pin is left unconnected. The other option is an AC-coupled 600 mV peak-to-peak signal, when the BIAS output is used to set the DC voltage of the MASTER CLK pin as shown in Fig. 12. The MASTER CLK pin on each slave GP1020 is not used and should be tied to VDD or VSS. SLAVE CLK 20MHz with 1:1 nominal mark:space ratio. Output from master GP1020, input to slave, using a bidirectional buffer controlled by MASTER/SLAVE. This signal is held low when the master chip is reset and starts to toggle within 200ns after MASTERRESET is released.
8
GP1020
INT OUT This output signal is a free running interrupt timebase which may be used to interrupt the microprocessor to initiate data transfer sufficiently often that no correlation results will be missed. The tracking loops rely on the microprocessor to adjust the DCO registers in response to signal changes so the rate of interaction must be sufficiently high. If the frequency of INT OUTis too high for the software to process then a polling scheme may be used, by inhibiting the interrupts (INT_MASK bit in TIMER_CNTL set low) and then periodically writing to STATUS_LATCH and reading the status registers to check if new data is available. The period of INT OUT is programmable; a typical value is 505*05s. During MASTERRESET the interrupt output is stopped and the pin is held LOW if in Intel mode, or HIGH if in Motorola mode. The active duration of INT OUT (HIGH for Intel, LOW for Motorola) is 252*525s, which should be more than adequate to ensure that the interrupt controller in the processor will have time to respond. INT IN This input signal is normally provided by the INT OUT output of a companion GP1020; in general the master drives the slave. It is used, when selected via the INT_SOURCE bit of the TIMER_CNTL register, to latch the state of the status bits. 100kHz/219kHz A clock output at either 100kHz or 219kHz which may be used to drive the microprocessor interrupt timer. The frequency is set by the level on CLKSEL (HIGH for 100kHz and LOW for 219kHz). MASTERRESET When MASTERRESET is set LOW , all the registers, accumulators and counters are cleared, except CHX_CNTL, which IS initialised to specific values (refer to detailed description of the registers for these values). When the device is held reset, by MASTERRESET set low, the following pins are driven as listed: MASTER CLK: This input may or may not be being externally driven during the reset. MASTERRESET internally gates MASTER CLK to ensure a well defined level on all clock lines until the release of MASTERRESET; the release of MASTERRESET must occur only when the input buffer is properly biased and the input signal is stable. SLAVE CLK: Configured as an input on slave devices and held LOW on master device. SAMP CLK: Held LOW. 100/219kHz: This output is held LOW when MASTER RESET is active (also LOW) and toggles to HIGH shortly after MASTERRESET is released, and then runs normally. D0-D15: High impedance. BITE CNTL: DISC OP: TIC OUT: INT OUT: LOW. LOW. LOW. This output is held LOW until interrupt inhibit is removed, when in Intel bus type mode, or is held HIGH until the inhibit is removed, when in Motorola bus type mode. (e.g. ARINC 743 may be wanted) or a simple reference time clock may be built. To synchronise TIME MARK to GPS time the first stage is to acquire the measurement data at any arbitrary TIC and then calculate the full navigation solution to give the time at that TIC. From this determine a later TIC at which to acquire data again such that after the navigation solution computation delay (typically a few TIC periods long) a further delay may be programmed into DOWN_COUNT_HI and _LO registers to start on the next TIC, to give TIME MARK at the required GPS whole second. This is rather a long process to get started, but once the first correct TIC choice and down counter delay are known the process can roll on with each TIC and delay calculation coming from the previous navigation solution. To get UTC instead of GPS time it is only neccessary to read the navigation message to get the number of whole seconds difference and add this to the calculated GPS time. A possible refinement is to calculate the oscillator drift over several measurements and use this to extrapolate a better value for the delay counter. The ultimate accuracy that can be achieved is very good, but to get this the crystal must both have high stability and be drift compensated in the software; in addition, the receiver front-end delay must be known and allowed for, and the delay through the output drivers and cables must be allowed for by using the MARKFBx pins. If, as is likely, Selective Availability is on it will be the main source of error in a well designed TIME MARK system, but better than one microsecond absolute accuracy is still possible. To reduce the effects of SA it is possible to use a stable rubidium reference oscillator and average the induced offsets over a long time to give very good peak errors of a few tens of nanoseconds. As the main purpose of the TIME MARK output is a timing reference signal at one pulse per second for the electronic systems in an airliner, it must be both accurate and known to be accurate. The accuracy is achieved by loading DOWN_COUNT_HI and _LO with the correct offset in 50ns units from the GPS measuring TIC. As the TIC rate is nominally 1ppm less than 10Hz, the DOWN_COUNT value should be expected to increase at around 1s per one second TIME MARK, a number change of 120 each pulse. This value will need continuous fine tuning to allow for the stable and variable crystal errors. Integrity is ensured in two ways; first, by using PROP_DELAY to check the delay through line drivers and to verify that a TIME MARK really did occur and, secondly, by having a complex handshake sequence so that any failure in the hardware will be detected by the microprocessor. The handshake sequence is: 1. Write to DOWN_COUNT_LO to arm the TIME MARK generator (this requires that DOWN_COUNT_HI is already written; as it rarely changes,this is often automatically true). 2. At next TIC the GP1020 will start DOWN_COUNT. 3. The GP1020 will give a TIME MARK pulse output and start the PROP_DELAY counter. 4. Feed TIME MARK back through MARK_FBx input to stop PROP_DELAY and to set MARK_FB_ACK in MEAS_STATUS_A 5. Read MEAS_STATUS_A, normally as part of the Measurement Data transfer protocol but, on this occasion, to also clear the overwrite protection on PROP_DELAY and to clear the MARK_FB_ACK bit. 6. Read PROP_DELAY, once MARK_FB_ACK has been set (and cleared) to give a stable value for the last delay. This also re-enables the TIME MARK generator ready for a repeat of step (1) to take effect. This may seem rather complicated, but is only needed once per second and so is little overhead if a simple system is all that is required. For a full accuracy system, the various register operations fit in with the computations needed to achieve full ARINC 743 specification.
TIME MARK The primary purpose of the TIME MARK output is to give a one pulse per second signal locked to UTC or GPS time. This may be followed by the correct time from the microprocessor and could be used as a reference by other navigation instruments
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GP1020
SATELLITE CODE SELECTION
This section describes the code selection for normal GPS and GLONASS operation; for INMARSAT codes and unusual techniques see full details in DETAILED DESCRIPTION OF REGISTERS section, under CHx_CNTL. The same section gives details of the other bits of CHx_CNTL. The satellite code to be used by each channel is set by the CHx_CNTL registers, which are addressed individually from the A8-A1 address bus by: 00H : Read/Write to Channel 1 10H : Read/Write to Channel 2 20H : Read/Write to Channel 3 30H : Read/Write to Channel 4 40H : Read/Write to Channel 5 50H : Read/Write to Channel 6 70H : Write only, to all channels simultaneously The one GLONASS code may be selected by setting bit 10 HIGH, otherwise this bit should be set LOW and bits 7 to 0 used to select one of the GPS Gold codes (see Table opposite). Bit setting 7654 3210 0001 0101 0010 0110 0011 0111 0100 1xx0 0000 1xx0 0001 1xx1 0000 0111 0001 1xx0 0010 1xx1 0001 0010 0010 0011 0100 0101 0101 0110 0110 0111 0111 1xx0 1xx0 1xx1 0000 0011 0001 0100 0010 0101 0011 0110 0100 0111 0101 1xx0 0000 0010 0011 0101 0100 0110 0101 0111 0110 1xx0 0111 1xx1 0000 0101 0001 0110 0010 0111 0011 1xx0 0100 1xx1 0011 1xx1 0000 0110 0001 0111 0011 1xx1 GPS PRN reference number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33* 34* = 37 35* 36* 37* = 34 Selected taps to be EXORed together 2 3 4 5 1 2 1 2 3 2 3 5 6 7 8 9 1 2 3 4 5 6 1 4 5 6 7 8 1 2 3 4 5 4 1 2 4 6 7 8 9 9 10 8 9 10 3 4 6 7 8 9 10 4 5 6 7 8 9 3 6 7 8 9 10 6 7 8 9 10 10 7 8 10
SOFTWARE REQUIREMENTS
The very wide variety of types of GPS or GLONASS receiver need to operate the correlator in different ways so, to accomodate this and also to allow dynamic adjustment of loop parameters, the GP1020 has been designed to use software for as many functions as possible. This flexibility means that the device cannot be used without a microprocessor closely linked to it, but as a processor is always needed to convert the output of the GP1020 into useful information this is not a significant limitation. The software associated with the GP1020 can be divided into two separate modules: one to acquire and track satellite signals to give pseudoranges and another to process these to give the navigation solution and format it in a form suitable for the user. For the Navigation Solution to be possible all of the pseudoranges must have exactly the same clock error, which can then be removed iteratively to give real ranges if sufficient satellites are tracked (3 if the height is known, otherwise 4). This need for exact matching of timing errors explains the need for all of the complicated synchronisation between all channels and between master and slaves. The following relates only to the signal processing aspects of the software, to acquire and track signals from up to six satellites per GP1020 and to obtain the pseudoranges and the navigation message. The operation of the navigation software is not dependent on the details of the correlator, and so does not need to be included in this data sheet. An on-chip interrupt time base INT OUT is provided to help implement a data transfer protocol between the microprocessor and the GP1020 at fixed time intervals, otherwise a software based polling scheme will be needed - the choice is set by the application. If INT OUT is used, and perhaps also if polling is used, the data transfer rate is about twice the correlation result rate for each channel, so many transfers will not give new data. Bus use can be reduced by examining the status registers before each transfer to see if new data is available and then only reading the data if it useful. It is important to note that the timing of each of the correlator channels will be locked to its own incoming signal and not to each other or to the microprocessor interrupts, so new data is generated asynchronously. The sampling instant of measurement data of all channels, however, is common to give a consistent navigation solution. In order to acquire lock to the satellites as quickly as possible, the data from the last fix should be stored as a starting point for the next fix. It is also useful to have a real-time clock built into the receiver to give a good estimate of GPS time for the next fix; the navigation solution can be used to measure clock drift and calculate a correction for the clock to overcome ageing. The
GPS Gold codes. *Note that these codes, 33 to 37, are reserved for non-satellite use only.
user's location (or a good estimate of it) along with the Almanac and the correct time will indicate which satellites should be searched for and may be used to find an estimate of Doppler effects, while the previous clock error is the best available estimate of the present clock error. If this information is not available then the receiver must scan a much wider range of values, which will greatly increase the time to lock. The satellite Clock Correction and Ephemeris are needed for the navigation solution, so if a recent set is held in memory the calculations may begin as soon as lock is achieved and not need to wait for the retransmission (18 to 36 seconds). This description applies to just one tracking channel but is the samd this is not necessarily the same as the other channels. The GP1020 contains four different types of registers:
* * * *
Control Registers which are used to program functions of the device. Status Registers which provide a status indication of the process taking place in the device. Accumulated Data Registers which provide the results of correlation with the C/A code every millisecond. This is the raw data used to acquire and track satellite signals. Measurement Data Registers which latch the carrier DCO phase, carrier cycle count, code DCO phase, 1 millisecond
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GP1020
epoch, and the 20 millisecond epoch count at every 9.09 or 100 milliseconds interval. This is the raw data used to compute pseudorange. 8. Once the GPS signal has been found, the code phase alignment, the carrier phase alignment and the Doppler and user clock bias compensations are still coarse. The code phase alignment is only within a half code chip, the carrier DCO is not in phase with the incoming signal and its frequency is still in error by up to the increment used for successive trials. The signal processing software must next use a pull-in algorithm to refine these alignments. There are many suitable types of algorithm to choose from, such as successive small steps until the error is too small to matter, like an analog PLL, or by using more complicated signal processing to estimate the errors and jump to a much better set of values. The signal pullin algorithm will then program CHx_CARR_INCR_LO/HI registers with more accurate values for the Carrier DCO. Corrections to the Gold code phase smaller than a half chip cannot be done by programming CHx_CODE_SLEW registers in the Code Generator, but should set CHx_CODE_INCR_LO/HI registers to steer the Code DCO and gradually bring the Gold code phase to the right value.
SOFTWARE SEQUENCE FOR ACQUISITION
Satellite signals seen by a GPS receiver are so weak that they are buried in the noise and can only be detected by correlation. The spectrum of each signal is spread, using 1023 chip Gold codes for GPS or a 511 chip maximal length code for GLONASS; to correlate them therefore, a locally generated code must be chosen to precisely match the spreading code type, rate, and phase. This pattern is then multiplied bit-by-bit with the incoming data stream and the results integrated over the code length to recover the signal. The process of signal acquisition is simply the matching of receiver settings to the actual signal values. To make matters more complicated the satellite carrier frequency is shifted a little by the Doppler effect due to the motion of the satellite, the user clock will drift randomly, and (in most situations) the signal to noise ratio is poor for some satellites. As a result, the software must be `wide-band' to find the signal and also `narrow-band' to reduce noise, leading to very different programs in different applications. For all tracking channels, the signal processing software needs the following sequence of activities: 1. Program CHx_CNTL register to select the desired GPS Gold code (PRN number) for the selected satellite and code type for the mode of the correlator dithering arm - it is often best, when in acquistion mode, to fix the dithering arm at early or at late and do a search in two phases at once and then switch to a tracking mode once a satellite is found. 2. Program CHx_CARR_INCR_LO and CHx_CARR_INCR_HI The values programmed into these two registers are concatenated and set the local oscillator frequency for the digital mixing performed in the GP1020 to bring the incoming 2-bit digitised signal down to baseband. The value to be programmed is equal to the nominal local oscillator frequency plus the estimated Doppler shift compensation plus the estimated user clock frequency drift compensation. 3. Program CHx_CODE_INCR_LO and CHx_CODE_INCR_HI The value to be programmed in these registers represents twice the nominal chipping rate of the C/A code (2.046 MHz) plus, if desired, a small compensation for the Doppler shift and for the user clock frequency drift. 4. Release the tracking channel reset by programming the RESET_CNTL Register with the proper value. This will cause the correlation process to start. 5. Obtain accumulated data from Accumulated Data Register readings. Several consecutive readings on the same tracking channel can be added to increase, at will, the integration period of the correlation. 6. Decide if the GPS signal has been found by comparing the correlation result with a threshold. If found then jump to a signal pull-in algorithm. Note that both in-phase and phase quadrature accumulated data have to be considered since at this time, the carrier DCO local oscillator phase is not necessarily in phase with the incoming GPS signal. 7. If the GPS signal has not been found, a new trial has to be made with different carrier DCO, code DCO, or Gold code phase programmings. Typically, both DCOs would be held constant while the Gold code phase is varied to try all of the 2046 half chip positions possible, then the carrier DCO would be programmed with slightly different values and the Gold code phase positions would again be scanned. The Gold code phase is varied by programming the CHx_CODE_SLEW Register and can be varied by increments of half a code chip.
SIGNAL TRACKING
The incoming GPS signal will exhibit a Doppler shift which varies with time due to the non-uniform motion of the satellite relative to the receiver, and the user clock bias is likely to also vary with time. The net result is that unless dynamic corrections are applied to the code and carrier DCOs, the GPS signal will be lost. This leads to two servo loops being required: one to maintain lock on the Gold code phase and a second to maintain lock on the carrier. With the GP1020 these servo loops are implemented in the signal processing software. The raw data used to steer the two servo loops is the Accumulated Data, which is output by the tracking channel at the rate of once per millisecond. The dithering arm Accumulated Data is used for the Gold code loop; some approaches use an `early minus late' Gold code to implement a null steering loop, others use a dithering code which alternates between a code one half chip late and a code one half chip early. In the GP1020, the dithering rate is 20 ms (20 code epochs) each way, starting with Early after a reset, when this type of code is selected through the CHx_CNTL register. The Gold code loop is closed by regularly updating the code DCO frequency using the CHx_CODE_INCR_LO/HI registers. The prompt arm Accumulated Data is used for the carrier phase loop (although the dithering arm may also be used). One approach consists of varying the carrier DCO phase in order to maintain all the correlation energy in the in-phase correlator arm and none in the phase quadrature correlator arm. The carrier phase loop is closed by regularly updating the carrier DCO frequency using the CHx_CARR_INCR_LO/HI registers.
DATA DEMODULATION
The C/A code is modulated with Space Vehicle (SV) data at 50 Baud to give the navigation message. This modulation is an exclusive-OR function of the C/A code with the SV data. This means that every 20 milliseconds (which is every 20 C/A code epochs), the C/A code phase will be reversed (shifted by 180 degrees) if the new data bit is different from the previous one. On the prompt arm, once the signal is being correctly tracked, such a data bit transition will change the sign of the accumulated data. Data demodulation can then be achieved in two stages: 1. Locate the instants of data bit transitions to identify which C/A code epoch corresponds to the beginning of a new data bit. This will allow initialisation of the GP1020 epoch counters by the signal processing software (through the CHx_1MS_ and 20MS- EPOCH registers) to count code epochs from 0 to 19 in phase with data bits. At each new cycle of the 1 ms epoch counter, the 20 ms epoch counter will increment.
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GP1020
2. Record the sign of accumulated data on the prompt arm for each data bit period of 20 ms, with filtering to reduce the effect of noise on the signal. Note that there is a sign ambiguity in the demodulation process in that it is not possible to tell which data bits are `0's and which are `1's from the signal itself. This ambiguity will be resolved at a later stage when the full Navigation Message is interpreted. Space Vehicle Navigation Message, which contains information on the GPS system time for the transmission of the current subframe; this is equal to term t2. The time information in the navigation message allows the receiver time to be initialised with a resolution of 20 milliseconds (one data bit period) but with knowledge of the precision to much better than one C/A code chip - a little less than 1 microsecond. As the timeof-flight from the satellite to the receiver is in the region of 60 to 80 milliseconds an improved first guess for local time could include an allowance for this delay to reduce the iteration time later. By using the data to time-tag the TIC, along with the values of the Epoch counter, the Code generator phase, and the Code clock phase it is possible to measure the time of the SV signal in local apparent time. This gives the value of t1 needed for the pseudorange measurement. The pseudorange can now be computed as t12t2. The error present in the time setting is the initial value of the user clock bias, with an allowance for the various counter phases. Once a Navigation Solution has been found the clock error is precisely known and may be used for future pseudorange calculations. Because the receiver clock drifts with time, the clock bias changes with time and must be tracked by the Navigation software.
PSEUDORANGE MEASUREMENT
The measurement data registers provide the raw data necessary to compute the pseudorange. This raw data is a sample, at a given instant set by the GP1020 TIC, of the 20 ms and 1 ms epoch counters, the C/A code phase counter and the code DCO phase. By definition, the pseudorange is expressed in time units and is equal to the satellite-to-receiver propagation delay plus the user clock bias. The user clock bias is first estimated (blind guessed is more likely with a cold start, but iteration then takes longer) and then obtained as a by-product of the navigation solution. The pseudorange is equal to the user's apparent local time of reception of the signal (t1) minus the GPS real time of transmission (t2). With the demodulated data, the software has access to the
12
GP1020
GP1020 REGISTER ADDRESSES AND CONTENT Overall Memory Map
The GP1020 internal registers are addressed using 8 address lines, A1 to A8. This section gives an overview of the register names with their addresses. A detailed memory map is shown in the Table of Registers. Address range (Hex) 00 to 07 10 to 17 20 to 27 30 to 37 40 to 47 50 to 57 70 to 77 Register Block accessed Access to control registers of tracking channel 1 Access to control registers of tracking channel 2 Access to control registers of tracking channel 3 Access to control registers of tracking channel 4 Access to control registers of tracking channel 5 Access to control registers of tracking channel 6 For write operations only. Access to all identical control registers of all tracking channels with one single operation. The same data gets written in these registers. Access to Accumulated Data and Measurement Data Status Access to In Phase and Quad Phase accumulated data registers and SBR (Status Bit Reset) commands of all tracking channels. Access to all identical SBR (Status Bit Reset) commands of all tracking channels with a single write operation. Access to measurement data registers of all tracking channels. For write operations only. Access to all identical measurement data registers of all tracking channels with one single operation. The same data gets written in these registers. Access to BITE interface, TIME_BASE_GEN, RESET_CNTL, signal selector and test registers.
80 to 83 84 to 9B 9C,9D A0 to B7 BC to BF
C0 to C8
Other addresses not used. Do not access these addresses. Note 1: Registers are not all READ/WRITE. To minimise the hardware, some addresses are shared between read-only and write-only registers having different functions. Refer to TABLE OF REGISTERS for more details.
TABLE OF REGISTERS
Address (Hex) 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 Read function CH1_CNTL CH1_TST_CODE_SLEW CH1_EPOCH_CHK CH1_SHIFT_REG not used not used not used not used not used not used not used not used not used not used not used not used CH2_CNTL CH2_TST_CODE_SLEW Register Write function CH1_CNTL CH1_SIG_SEL CH1_CODE_INCR_HI CH1_CODE_INCR_LO CH1_CARR_INCR_HI CH1_CARR_INCR_LO CH1_TST_CODE_PHASE CH1_TST_CYCLE not used not used not used not used not used not used not used not used CH2_CNTL CH2_SIG_SEL Continued...
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GP1020
TABLE OF REGISTERS (continued)
Address (Hex) 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37 38 39 3A 3B 3C 3D 3E 3F 40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F Read function CH2_EPOCH_CHK CH2_SHIFT_REG not used not used not used not used not used not used not used not used not used not used not used not used CH3_CNTL CH3_TST_CODE_SLEW CH3_EPOCH_CHK CH3_SHIFT_REG not used not used not used not used not used not used not used not used not used not used not used not used CH4_CNTL CH4_TST_CODE_SLEW CH4_EPOCH_CHK CH4_SHIFT_REG not used not used not used not used not used not used not used not used not used not used not used not used CH5_CNTL CH5_TST_CODE_SLEW CH5_EPOCH_CHK CH5_SHIFT_REG not used not used not used not used not used not used not used not used not used not used not used not used Register Write function CH2_CODE_INCR_HI CH2_CODE_INCR_LO CH2_CARR_INCR_HI CH2_CARR_INCR_LO CH2_TST_CODE_PHASE CH2_TST_CYCLE not used not used not used not used not used not used not used not used CH3_CNTL CH3_SIG_SEL CH3_CODE_INCR_HI CH3_CODE_INCR_LO CH3_CARR_INCR_HI CH3_CARR_INCR_LO CH3_TST_CODE_PHASE CH3_TST_CYCLE not used not used not used not used not used not used not used not used CH4_CNTL CH4_SIG_SEL CH4_CODE_INCR_HI CH4_CODE_INCR_LO CH4_CARR_INCR_HI CH4_CARR_INCR_LO CH4_TST_CODE_PHASE CH4_TST_CYCLE not used not used not used not used not used not used not used not used CH5_CNTL CH5_SIG_SEL CH5_CODE_INCR_HI CH5_CODE_INCR_LO CH5_CARR_INCR_HI CH5_CARR_INCR_LO CH5_TST_CODE_PHASE CH5_TST_CYCLE not used not used not used not used not used not used not used not used Continued...
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GP1020
TABLE OF REGISTERS (continued)
Address (Hex) 50 51 52 53 54 55 56 57 58 59 5A 5B 5C 5D 5E 5F 60 to 6F 70 71 72 73 74 75 76 77 78 79 7A 7B 7C 7D 7E 7F 80 81 82 83 84 85 86 87 88 89 8A 8B 8C 8D 8E 8F 90 91 92 93 94 95 96 97 98 99 Read function CH6_CNTL CH6_TST_CODE_SLEW CH6_EPOCH_CHK CH6_SHIFT_REG not used not used not used not used not used not used not used not used not used not used not used not used not used not used not used not used not used not used not used not used not used not used not used not used not used not used not used not used not used MEAS_STATUS_A MEAS_STATUS_B ACCUM_STATUS_A ACCUM_STATUS_B CH1_I_DITH CH1_Q_DITH CH1_I_PROMPT CH1_Q_PROMPT CH2_I_DITH CH2_Q_DITH CH2_I_PROMPT CH2_Q_PROMPT CH3_I_DITH CH3_Q_DITH CH3_I_PROMPT CH3_Q_PROMPT CH4_I_DITH CH4_Q_DITH CH4_I_PROMPT CH4_Q_PROMPT CH5_I_DITH CH5_Q_DITH CH5_I_PROMPT CH5_Q_PROMPT CH6_I_DITH CH6_Q_DITH Register Write function CH6_CNTL CH6_SIG_SEL CH6_CODE_INCR_HI CH6_CODE_INCR_LO CH6_CARR_INCR_HI CH6_CARR_INCR_LO and ADD_DAT_TST CH6_TST_CODE_PHASE CH6_TST_CYCLE not used not used not used not used not used not used not used not used not used ALL_CNTL ALL_SIG_SEL ALL_CODE_INCR_HI ALL_CODE_INCR_LO ALL_CARR_INCR_HI ALL_CARR_INCR_LO ALL_TST_CODE_PHASE ALL_TST_CYCLE not used not used not used not used not used not used not used not used STATUS LATCH not used not used not used CH1_MEAS_RST CH1_ACCUM_RST not used not used CH2_MEAS_RST CH2_ACCUM_RST not used not used CH3_MEAS_RST CH3_ACCUM_RST not used not used CH4_MEAS_RST CH4_ACCUM_RST not used not used CH5_MEAS_RST CH5_ACCUM_RST not used not used CH6_MEAS_RST CH6_ACCUM_RST Continued...
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GP1020
TABLE OF REGISTERS (continued)
Address (Hex) 9A 9B 9C 9D 9E 9F A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 AA AB AC AD AE AF B0 B1 B2 B3 B4 B5 B6 B7 B8 B9 BA BB BC BD BE BF C0 C1 C2 C3 C4 C5 C6 C7 C8 C9 to FF Read function CH6_I_PROMPT CH6_Q_PROMPT not used not used not used not used CH1_EPOCH_A CH1_EPOCH_B CH1_CARR_DCO_PHASE CH1_CARR CYCLE CH2_EPOCH_A CH2_EPOCH_B CH2_CARR_DCO_PHASE CH2_CARR CYCLE CH3_EPOCH_A CH3_EPOCH_B CH3_CARR_DCO_PHASE CH3_CARR CYCLE CH4_EPOCH_A CH4_EPOCH_B CH4_CARR_DCO_PHASE CH4_CARR CYCLE CH5_EPOCH_A CH5_EPOCH_B CH5_CARR_DCO_PHASE CH5_CARR CYCLE CH6_EPOCH_A CH6_EPOCH_B CH6_CARR_DCO_PHASE CH6_CARR CYCLE not used not used not used not used not used not used not used not used RESET_CNTL BITE RTC_DELAY PROP_DELAY_LO PROP_DELAY_HI STAT_CHK_SIGN STAT_CHK_MAG ADD_DAT_TST not used not used Register Write function not used not used ALL_MEAS_RST ALL_ACCUM_RST not used not used CH1_1MS_EPOCH CH1_PRESET_PHASE CH1_CODE_SLEW CH1_20MS_EPOCH CH2_1MS_EPOCH CH2_PRESET_PHASE CH2_CODE_SLEW CH2_20MS_EPOCH CH3_1MS_EPOCH CH3_PRESET_PHASE CH3_CODE_SLEW and ADD_DAT_TST CH3_20MS_EPOCH CH4_1MS_EPOCH CH4_PRESET_PHASE CH4_CODE_SLEW CH4_20MS_EPOCH CH5_1MS_EPOCH CH5_PRESET_PHASE CH5_CODE_SLEW CH5_20MS_EPOCH CH6_1MS_EPOCH CH6_PRESET_PHASE CH6_CODE_SLEW CH6_20MS_EPOCH not used not used not used not used ALL_1MS_EPOCH ALL_PRESET_PHASE ALL_CODE_SLEW ALL_20MS_EPOCH RESET_CNTL BITE TIMER_CNTL DOWN_COUNT_HI DOWN_COUNT_LO STAT_CHK_SEL not used ADD_DAT_TST TDATA_DUTY_CYCLE not used
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GP1020
DETAILED DESCRIPTION OF REGISTERS
The registers are listed in alphabetical order and not in address order to allow easy reference to each section.
ACCUM_STATUS_B Read Address 83H
Register bit mapping Bit LSB 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 MSB 15 Bit name CH1_MISSED_ACCUM CH2_MISSED_ACCUM CH3_MISSED_ACCUM CH4_MISSED_ACCUM CH5_MISSED_ACCUM CH6_MISSED_ACCUM not used not used CH1_OVFL_ACCUM CH2_OVFL_ACCUM CH3_OVFL_ACCUM CH4_OVFL_ACCUM CH5_OVFL_ACCUM CH6_OVFL_ACCUM not used not used
ACCUM_STATUS_A Read Address 82H
Register bit mapping Bit LSB 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 MSB 15 Bit name CH1_NEW_ACCUM_DATA CH2_NEW_ACCUM_DATA CH3_NEW_ACCUM_DATA CH4_NEW_ACCUM_DATA CH5_NEW_ACCUM_DATA CH6_NEW_ACCUM_DATA not used not used CH1_EARLY_LATEB CH2_EARLY_LATEB CH3_EARLY_LATEB CH4_EARLY_LATEB CH5_EARLY_LATEB CH6_EARLY_LATEB not used NEW STAT_DATA
REGISTER OPERATION ACCUM_STATUS_A is a latch register containing the state of status bits prevailing at time of sampling. The status bits are sampled and latched on the positive edge of every INT OUT or INT IN signal. They can also be sampled and latched on request by performing a write operation to STATUS_LATCH (location 80H). Latching the status bits ensures glitch-free reading of ACCUM_STATUS_A. BIT DESCRIPTION The following bits are all active HIGH: CHx_NEW_ACCUM_DATA status bit indicates if there is new accumulated data available to be read. Each individual bit can be cleared with a write operation at CHx_ACCUM_RESET location or by disabling the propagation of clocks (CHx_RSTB bits of RESET_CNTL). This also releases the overwrite protection. Each bit is also cleared on the trailing edge of a read of the associated Q_PROMPT register. If new accumulated data becomes available after ACCUM_STATUS_A bits have been latched, the overwrite protection is not cleared while reading the Q_PROMPT register and the CHx_NEW_ACCUM_DATA bit will be set at the next latching of ACCUM_STATUS_A. CHx_EARLY_LATEB status bit indicates whether the accumulated data on the dithering arm of the tracking channel results from correlation with early or late code. A HIGH indicates an EARLY code and a LOW indicates a LATE code. Each individual bit is updated at each DUMP when the overwrite protection is not active. When the Early-Minus-Late code is selected for a particular channel, this status bit has no meaning. NEW_STAT_DATA status bit when HIGH indicates that new statistical data is available in the STAT_CHK_SIGN and STAT_CHK_MAG registers. It is cleared when a STAT_CHK_MAG read operation is performed if a valid state had been latched previously or by a write operation at ALL_ACCUM_RESET location. The first statistical data after a power up is not representative and should be cleared. All status bits are reset by a hardware or software master reset.
REGISTER OPERATION ACCUM_STATUS_B bits are sampled and latched on the positive edge of every INT OUT or INT IN signal. They can also be sampled and latched on request by performing a write operation to STATUS_LATCH (location 80H). BIT DESCRIPTION CHx MISSED_ACCUM status bit indicates if there has been missed accumulated data. When active HIGH, this status bit is latched until (i) a master reset (hardware or software) or (ii) a write operation to CHx_ACCUM_RESET with don't care data or (iii) the propagation of clocks is disabled (CHx_RSTB bits of RESET_CNTL). CHx_OVFL_ACCUM status bit indicates if there has been an overflow in any of the channel accumulated data registers. This bit is active HIGH and is updated at each DUMP when the overwrite protection is not active. It gets reset whenever the associated CHx_ACCUM_RESET is written into with don't care data or upon a master reset (hardware or software) or by disabling the propagation of clocks (CHx_RSTB bits of RESET_CNTL).
ADD_DAT_TST Read/Write Address C7H
This register is used to test the address bus and data bus hardware connections to the inputs of the chip. It allows the system to verify that there is no short between pins or input lines in the chip or on the board. Register bit mapping Bit 15 to 8 7 to 0 Description Contents of address bus or most significant bits of data bus. Contents of least significant bits of data bus.
REGISTER OPERATION This register is a read/write register. Upon a master reset (software or hardware) the register is cleared. When a write is performed at address AAH or 55H the most significant bits of the register will be loaded with the address bus value present on the bus, AAH or 55H if the address bus is working properly and the least significant bits of the register will keep their previous value.
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GP1020
When a write is performed at address C7H the register will be loaded with the data bus value present on the bus. When a read operation is performed to C7H it reads all the bits previously loaded. It is recommended that the test is performed as follows in order to verify that the address and data bus operate properly. Address Bus Test: bits are don't * Write to address 55 (the dataat address C7 care) 8 least significant bits (the * Read the mostare 00 if no access had been done to the significant bits
H H H
* *
address C7H). If the value is not 5500H a problem is detected on the address bus. Write to address AAH (the data bits are don't care) Read the most significant bits at address C7H. If the value is not AA00H a problem is detected on the address bus. NOTE : When writing to addresses 55H and AAH, the CH6_CARR_INCR_LO and CH3_CODE_SLEW registers will also be written into with the values on the data bus.
self-test signal generator is disabled and TSIGN and TMAG output pins are held LOW. When active the self-test signal generator is enabled and TSIGN and TMAG output pins are toggling. The injection back into the input of the tracking channels is controlled by CHx_SIGNAL_SEL. SELF_TEST_SOURCE: When LOW, the tracking channel 1 is used as a signal source for the self-test signal generator. When HIGH, the tracking channel 2 is used as a signal source for the self-test signal generator. MEANDER: When HIGH, the self-test generator will modulate the data bit stream with a meander. This is required when GLONASS operation has to be tested. CARR_MIX_ENB: When LOW, all carrier mixers operate normally. When HIGH, all carrier mixers are disabled and the incoming sign and magnitude data passes through without being affected.
CHx_ACCUM_RESET Write Addresses 85, 89, 8D, 91, 95, 99H and ALL_ACCUM_RESET Write Address 9DH
These are write-only locations provided to allow resetting of all the status bits associated with a given channel in ACCUM_STATUS_A and ACCUM_STATUS_B. ALL_ACCUM_RESET access will also clear the NEW_STAT_DATA flag in ACCUM_STATUS_B register. When these locations are written into, the data is don't care. But if the CNTTESTMODE bit (CHx_20MS_EPOCH register) is active, G1 and G2 registers will be set at the 1023rd chip of the code sequence. This operation accelerates the test process by generating accumulated data and status bits when the code steps to the first chip and so generating a DUMP in the associated channel.
Data Bus Test:
* Write 5555 to address C7 C7 . If the value is not 5555 * Read the register at address data bus. a problem is detected on the Write AAAA to * Read the registeraddress C7C7 . If the value is not AAAA at address * a problem is detected on the data bus.
H H H H H H
H
H
BITE Read/Write Address C1 H
Register bit mapping Bit 0 1 2 3 4 5 6 7 8 Description BITECNTL DISCOP PLL_LOCKA (state) PLL_LOCKB (negative transition) GLONASS BIT SELF_TEST_EN SELF_TEST_SOURCE MEANDER CARR_MIX_ENB
CHx_CARR_CYCLE Read Addresses A3, A7, AB, AF, B3, and B7H
This register contains the 16 more significant bits of a variable containing the number of CARRIER DCO cycles that occurred during the last TIC period ending at a TIC. The value is sampled and latched on the TIC. While reading measurement data associated with a given channel, CHx_CARR_CYCLE must be read last because the trailing edge of a read to this register will release the overwrite protection mechanism of measurement data for this channel. CARR_CYCLE: PRINCIPLE OF OPERATION In the CHx_CARR_CYCLE register and counter a TIC generates two consecutive actions: 1. It latches the 16 more significant bits of the cycle up counter into CARR_CYCLE and the 2 less significant bits into CARR_DCO_PHASE. 2. It resets the cycle up counter. After each TIC, every time the carrier DCO accummulator generates an OVERFLOW as a result of a carrier cycle being completed, the cycle up counter counts up by one. The number of bits needed for the counter was established as follows: For GPS, the nominal CARRIER DCO frequency with no Doppler and no oscillator drift compensation is 1*405396825 MHz, so in 100 ms, there will be about 140,540 cycles. For GLONASS signals, the carrier DCO frequency wil vary depending on the particular satellite being tuned, between 1*429 - 0*6 MHz and 1*429 + 0*6 MHz, a maximum of 2*029 MHz, giving 202,900 cycles in 100 ms. The maximum number of cycles, CARR_COUNT MAX, will also depend on the maximum Doppler and oscillator drift compensation to be allowed for, hence the counter must be able to count to a number greater than 140,540 or 202,900. The highest frequency required is then 2*029 MHz plus a few
BIT DESCRIPTION BITECNTL bit: Drives the BITE input of the GP1010. Set inactive LOW by a Master Reset. When HIGH, the GP1010's PLL is unlocked and the 40 MHz signal becomes unstable. The GP1020 should be put into hardware master reset mode for the time needed to allow the GP1010's 40 MHz output to stabilise. DISC O/P: Discrete output with no specific function. LOW at power up and its state will follow the value written in the BITE register. PLL_LOCKA: input from GP1010, Read only, to indicate the state of the PLL LOCK signal; a HIGH indicates a locked condition. This discrete input can be used for other purposes. PLL_LOCKB: input from GP1010, indicates that a negative transition of the PLL LOCK signal (from locked to unlocked state) has been detected and latched in the GP1020. A HIGH indicates a negative transition. This bit is cleared by the trailing edge of a read to BITE register operation. GLONASS BIT: TEST input from GLONASS front end. A HIGH on this pin sets register bit HIGH. This discrete input can also be used for other purposes. SELF_TEST_EN: active HIGH. When inactive (LOW) the
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GP1020
DATA LOAD
TIC
CARRIER DCO ACCUMULATOR
ACCUMULATOR OVERFLOW EN CLK RESET
CYCLE UP COUNTER
2 16 LATCH LATCH
CARR_CYCLE REGISTER
CARR_DCO_PHASE REGISTER
ENABLE DATA BUS
Fig. 13 CHx_CARR_CYCLE block diagram
tens of kilohertz to allow for oscillator drift and Doppler compensation. An 18 bit counter will cover up to 262,143 cycles, which is more than adequate. REGISTER CONTENTS RANGE CHx_CARR_CYCLE is a 16 bit register, unsigned, and the validity range of the data is 0 to 21621. CHx_CARR_CYCLE content is protected by the overwrite protection mechanism of measurement data. Thus for an overwrite to occur, either the associated CHx_NEW_MEAS_DATA status bit has to be cleared or CHx_CARR_CYCLE itself has to be read.
CHx_CARR_INCR_HI & CHx_CARR_INCR_LO and ALL_CARR_INCR_HI & ALL_CARR_INCR_LO Write Addresses 04 & 05, 14 & 15, 24 & 25, 34 & 35, 44 & 45, 54 & 55 and 74 & 75H
Register bit mapping Bit CARR_INCR_HI 9 to 0 CARR_INCR_LO 15 to 0 Description More significant bits of the Carrier DCO phase increment. Less significant bits of the Carrier DCO phase increment.
CHx_CARR_DCO_PHASE Read Addresses A2, A6, AA, AE, B2, B6
Register bit mapping Bit 9 to 0 Description Most significant bits of CHx_CARR_DCO phase accumulator. The weight of the least significant bit is 2p/1024 radian. These bits form an unsigned integer valid from 0 to 1023. CHx_CARR_DCO_PHASE provides the sub-cycle integrated phase measurement information and therefore complements the information given by CHx_CARR_CYCLE Least significant bits of the number of carrier DCO cycles that occurred during the last TIC period ending at a TIC. The value is sampled and latched on the TIC. Not used.
REGISTER OPERATION The registers CARR_INCR_LO and CARR_INCR_HI are combined to form the 26 bits of the CARR_INCR register, the carrier DCO phase increment. Both registers are write-only registers and can be written to at any time. The first write must be performed on CARR_INCR_HI and the second write on CARR_INCR_LO. The written value is latched in the CARR_INCR register on the trailing edge of a write to CARR_INCR_LO. It is possible to perform a write only to CARR_INCR_LO register if the CARR_INCR_HI value does not need to be updated. The DCO adder is 27 bits wide and the LSB of the INCR register represents a step given by: Min. Step Freq. = (40MHz/7)32227 = 42*57475 milliHertz and the output frequency is: Freq. out = CHx_CARR_INCR reg. value3Min. Step Freq. The nominal value of the CHx_CARR_INCR register for GPS is 01F7 B1B9H (to get a carrier at 1*405396825 MHz when the GP1010 clock signal is at 40 MHz).
11 and 10
15 to 12
The register value is latched on a TIC and protected from overwrite by the overwrite protection mechanism of measurement data.
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GP1020
CHx_CODE_INCR_HI & CHx_CODE_INCR_LO and ALL_CODE_INCR_HI & ALL_CODE_INCR_LO Write Addresses 02 & 03, 12 & 13, 22 & 23, 32 & 33, 42 & 43, 52 & 53 and 72 & 73H
Register bit mapping Bit Description CODE_INCR_LO. The written value is latched in the CODE_INCR register on the trailing edge of a write to CODE_INCR_LO. It is possible to perform a write only to CODE_INCR_LO register if the CODE_INCR_HI value does not need to be updated. The DCO adder is 26 bits wide and the LSB of the INCR register represents a step given by: Min. Step Freq. = (40MHz/7)32226 = 85.14949 milliHertz and the output Frequency is: Freq. out = CHx_CODE_INCR reg. value3Min. Step Freq. NOTE: The CODE DCO drives the CODE GENERATOR to give half-chip time steps and so must be programmed to twice the required chip rate. This means that the chip rate resolution is 42*57475 milliHertz. The nominal value of the CHx_CODE_INCR register for GPS is 016E A4A8H (to get a chip rate of 1.023MHz when the GP1010 clock signal is at 40 MHz).
CODE_INCR_HI 8 to 0 More significant bits of the Code DCO phase increment. CODE_INCR_LO 15 to 0 Less significant bits of the code DCO phase increment. REGISTER OPERATION The registers CODE_INCR_LO and CODE_INCR_HI are combined to form the 25 bits of the CODE_INCR register, the code DCO phase increment. Both registers are write-only registers and can be written to at any time. The first write must be performed on CODE_INCR_HI and the second write on
CHx_CNTL and ALL_CNTL Read/Write Addresses 00, 10, 20, 30, 40, 50, and 70 H
Register bit mapping Bit 7 to 0 9 to 0 9 and 8 Operation mode of CHx_CNTL reg. (Set by bit 15) MODE1 MODE2 MODE1 Description C/A CODE SELECTION FUNCTION (see details below) CODESEL(0:1):selects the apppropriate code to be shifted out of the dithering arm output of the code generator as follows: 9=0 9=0 9=1 9=1 10 11 MODE1&2 MODE1&2 8 = 0 Early code 8 = 1 Late code 8 = 0 Dithering code 8 = 1 Early minus late code
GLO/GPSB: Selects the code type to be generated. GLONASS C/A code when HIGH, GPS or INMARSAT C/A code when LOW. CODE_OFF/ONB: When LOW, the code is output normally, but when HIGH, the Prompt, Early and Late codes are held HIGH (no effect on the mixer outputs) and the Early-minus-late code is held LOW to mask mixer outputs and force I&D input values to 0. PRESET/UPDB: While HIGH, Programs the channel to Preset mode, or while LOW, programs the channel to Update mode. not used - don't care CODESEL(0:1) As bits 9 and 8 MODE1. MODE: When LOW the CNTL register is in MODE1 (power up condition) and when HIGH in MODE2. When in MODE1, the selection of a C/A code is done by selecting two taps of the G2 register, but in MODE2 by presetting the value of the G2 register. The function of bits 8 and 9 will change depending on the MODE.
12 14 and 13 14 and 13 15
MODE1&2 MODE1 MODE2 ----
REGISTER OPERATION CHx_CNTL can be written into at any time and any modification to its content is effective immediately (within 250 ns) while in UPDATE mode, or for all bits except PRESET/UPDB at the next TIC while in PRESET mode. Before reading the content of this register, it is necessary to wait 250 ns after the last write
operation when in UPDATE mode. Only the PRESET bit is available immediately but it is cleared 150ns after the PRESET sequence has taken place (at the TIC following the initialisation of CHx_20MS_EPOCH register). It is important to program this register first when starting a PRESET initialisation sequence.
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GP1020
C/A CODE SELECTION The CHx_CNTL register allows two different modes of programming the CODE GENERATOR : MODE 1: select the appropriate taps of G2 to generate the GPS C/A code. MODE 2: set the G2 register with the appropriate pattern to generate the GPS or INMARSAT C/A codes. NOTE: When in MODE 2, the G2 register should be loaded with a value representing its state at the time of the second chip. The difference between the two modes of programming the C/A code is that MODE 2 allows the CODE GENERATOR to synthesise the 8 INMARSAT C/A codes and MODE 1 does not, but is more straightforward. The following table gives the pattern of bits 3 to 0 or 7 to 4 to select a particular tap (used in MODE 1 of the CHx_CNTL register) : Bit Pattern 0000 0001 0010 0011 0100 0101 0110 0111 1xx0 1xx1 Tap 1 2 3 4 5 6 7 8 9 10 MODE 1 bit setting 7 to 0 0000 0010 0011 0101 0100 0110 0101 0111 0110 1xx0 0111 1xx1 0000 0101 0001 0110 0010 0111 0011 1xx0 0100 1xx1 0011 1xx1 0000 0110 0001 0111 0011 1xx1 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a MODE 2 bit setting 9 to 0 267H 120H 270H 0E0H 1C0H 380H 22BH 056H 0ACH 158H 2B0H 058H 18BH 316H 058H 2C4H 10AH 3E3H 0F8H 25FH 1E7H 2B5H 10EH
GPS PRN signal no. 23 24 25 26 27 28 29 30 31 32 33 34 * 35 36 37 * 201 202 205 206 207 208 209 211
Selected taps 1 EXOR 3 4 EXOR 6 5 EXOR 7 6 EXOR 8 7 EXOR 9 8 EXOR 10 1 EXOR 6 2 EXOR 7 3 EXOR 8 4 EXOR 9 5 EXOR 10 4 EXOR 10 1 EXOR 7 2 EXOR 8 4 EXOR 10 n/a n/a n/a n/a n/a n/a n/a n/a
The table below shows the bit setting required to select the appropriate taps which will decode the 37 possible GPS PRN signal numbers when in MODE 1 and the bit setting required to set the G2 register in the second chip state for all GPS and INMARSAT C/A codes when in MODE 2. Note that the list does not show all the possible tap and bit setting combinations. Tap combinations which are not listed can also be used if required. GPS PRN signal no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 MODE 1 bit setting 7 to 0 0001 0101 0010 0110 0011 0111 0100 1xx0 0000 1xx0 0001 1xx1 0000 0111 0001 1xx0 0010 1xx1 0001 0010 0010 0011 0100 0101 0101 0110 0110 0111 0111 1xx0 1xx0 1xx1 0000 0011 0001 0100 0010 0101 0011 0110 0100 0111 0101 1xx0 Selected taps 2 EXOR 6 3 EXOR 7 4 EXOR 8 5 EXOR 9 1 EXOR 9 2 EXOR 10 1 EXOR 8 2 EXOR 9 3 EXOR 10 2 EXOR 3 3 EXOR 4 5 EXOR 6 6 EXOR 7 7 EXOR 8 8 EXOR 9 9 EXOR 10 1 EXOR 4 2 EXOR 5 3 EXOR 6 4 EXOR 7 5 EXOR 8 6 EXOR 9 MODE 2 bit setting 9 to 0 3F6H 3ECH 3D8H 3B0H 04BH 096H 2CBH 196H 32CH 3BAH 374H 1D0H 3A0H 340H 280H 100H 113H 226H 04CH 098H 130H 260H
*C/A Codes 34 and 37 are common NOTE: PRN sequences 33 to 37 are reserved for other uses (e.g. ground transmitters). The table below lists the required setting of the register bit 0 to generate the GLONASS C/A code or the GLONASS-like test C/A code. Note that bit 10 must be HIGH to select GLONASS rather than GPS codes. Bit 0 setting MODE 1 & 2 0 1 Code type Selected G1 taps
GLONASS 5 EXOR 9 GLONASS TEST 3 EXOR 5 EXOR 6 EXOR 9
In update mode, the C/A code generated by the CODE GENERATOR can be changed at any time but the next accumulated data following the command will not be valid. The MODE bit cannot be modified without disabling the clock phases when in UPDATE mode otherwise the C/A code generated will not be valid. This is not the case when starting a PRESET sequence. To provide a clean switch between GLONASS and GPS modes of operation for a specific channel, it is necessary to proceed as follows: Disable propagation of the clock phases to this tracking channel by selecting the appropriate bit in the RESET_CNTL register, then select the desired mode of operation GLONASS or GPS and re-enable the propagation of the clock phases. If the clock phases propagation are not disabled, the next accumulated data will not be valid. When the dithering code has been selected, the dithering arm will use the EARLY code for a period of 20 C/A codes, the LATE code for the next 20 C/A codes and this process of dithering between EARLY and LATE code will be repeated indefinitely. The dithering arm will use the EARLY code for the first 20 ms EPOCH following a SLEW or a PRESET operation. Upon MASTERRESET, CHx_CNTL bits are set to the states given in the following Table.
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GP1020
Bit 7 to 0 9 and 8 10 11 12 14 and 13 15 03H 00 0 0 0 00 0 State Description
GPS PRN No. 17 selected. Early Code on the dithering arm. GPS C/A CODE CODE ON UPDATE MODE N/A (MODE1) MODE1
CHx_CODE_SLEW and ALL_CODE_SLEW Write Addresses A2, A6, AA, AE, B2, B6 and BEH
Register bit mapping Bit 10 to 0 Description Unsigned integer ranging from 0 to 2047 representing the number of code half chips to be slewed after the next DUMP if in UPDATE MODE or after the next TIC, if in PRESET MODE. Since there are only 2046 half chips in a GPS C/A code, a programmed value of 2047 is equivalent to a programmed value of 1 but the next DUMP event will take place 1 ms later. For the GLONASS code a similar wraparound will occur at 1023 and 2045. The CHx_CODE_SLEW register can be written to at any time. If two accesses have taken place before a DUMP in UPDATE mode or before a TIC when in PRESET mode, the latest value will be used at the next slew operation. When the slew process is being executed, a write access to the CHx_CODE_SLEW register will cause the transfer of this new value into the counter and will be used immediately. The result is not predictable. This situation should be avoided by synchronising the access with the associated CHx_NEW_ACCUM_DATA status bit. Slew timing details are shown in Figs. 14 and 15.
1023 CHIPS
1025 CHIPS
DUMP: TIME
t1
C/A CODE CHIP NO. :
t1: Load 4 in the CHx_CODE_SLEW register = 2 chips delay.

1021 1022 1023 1 1 1 2 3
Fig. 14 SLEW in UPDATE mode
1023 CHIPS
1024*5 CHIPS
DUMP: TIME
t1
C/A CODE CHIP NO. :
t2
98 99 100 1
t3
t1: Set the PRESET mode (Bit 12 in CHx_CNTL register) t2: Load 3 in the CHx_CODE_SLEW register (=1*5 chips delay) t3: TIC event

1 1 2 3 4
Fig. 15 SLEW in PRESET mode
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GP1020
CHx_EPOCH_A Read Addresses A0, A4, A8, AC, B0, B4H
This register contains the variables as detailed below. Register bit mapping Bit 15 to 11 Description CHx_1MS_EPOCH: The one millisecond epoch counter value sampled at TIC event. Its valid range is 0 to 19. CHx_CODE_PHASE: Represents the code phase of the code generator when sampled and latched on a TIC, expressed as a number of half code chips. It ranges from 0 to 2045 when a GPS C/A code is generated and from 0 to 1021 when a GLONASS C/A code is generated. Bit 15 to 2
CHx_I_DITH, CHx_Q_DITH, CHx_I_PROMPT, CHx_Q_PROMPT 24 consecutive Read Addresses 84 to 9BH
Register bit mapping Description Accumulated data registers, which are loaded on each Dump event with the I&D accumulator results. Not used, held LOW. Instantaneous value of the over/underflow flag (for test purposes). Normally LOW, but HIGH if the data being accumulated in the I&D accumulator has reached the over/underflow condition.
10 to 0
1 0
CHx_EPOCH_A content is protected from overwrite by the overwrite protection mechanism of measurement data.
CHx_EPOCH_B Read Addresses A1, A5, A9, AD, B1, B5H
The register contains two variables as detailed below: Register bit mapping Bit 15 and 14 13 to 8 Not used. CHx_20MS_EPOCH: Contains the 20 millisecond epoch counter value sampled at TIC event. Its valid range is from 0 to 49. CHx_CODE_DCO_PHASE: Contains the eight most significant bits of the code DCO phase accumulator sampled at TIC event. The weight of the least significant bit is 2p/256 radians, 2p being 1/2 code chip. The byte is an unsigned integer valid from 0 to 255. Description
7 to 0
REGISTER OPERATION These registers are read only registers; they can be read at any time and their content is protected by the overwrite protection mechanism of accumulated data. The CHx_I_PROMPT and CHx_Q_PROMPT contain the accumulated data taken on the Prompt arm. The CHx_I_DITH and CHx_Q_DITH contain the accumulated data taken on the Dithering arm. The overwrite protection mechanism is released by reading the CHx_Q_PROMPT register. The values contained in the registers are 2's complement values with the valid range of the data from 213 for negative numbers to (213 21) for positive numbers. When an over/ underflow condition is flagged (CHx_OVFL_ACCUM bit in ACCUM_STATUS_B set HIGH) the contents of the registers for this arm will be the last I&D accumulator values before the over/ underflow condition happened. If bit 15 is LOW it is an overflow and if bit 15 is HIGH it is an underflow. Bits 0 of the 24 accumulated data registers have no link with the other data in these registers. When HIGH, each of these bits indicates that the data being accumulated in the I&D has reached the maximum value (positive or negative) of the accumulator and this value will be available at the next DUMP.
CHx_EPOCH_B content is protected from overwrite by the overwrite protection mechanism of measurement data.
CHx_MEAS_RST and ALL_MEAS_RST Write Addresses 84, 88, 8C, 90, 94, 98 and 9CH
A write to this location with don't care data resets all measurement data status bits contained in both MEAS_STATUS_A and MEAS_STATUS_B registers. It also clears any active overwrite protection on measurement data. ALL_MEAS_RST access will also clear the MARK_FB_ACK and the RTC_TIC_ACK flags in MEAS_STATUS_A register and the associated overwrite protections.
CHx_EPOCH_CHK Read Addresses 02, 12, 22, 32, 42, 52H
This register contains the instantaneous value of CHx_1MS_EPOCH and CHx_20MS_EPOCH. It can be used to verify if the Epoch counters have properly been initialised by the software since the timing is critical for the initialisation operation. Its value is not latched and is updated on the occurence of a DUMP. This register should be read only when there is no possibility of getting a DUMP during the read cycle. Register bit mapping Bit 15 to 13 12 to 8 7 6 5 to 0 Description Not used. Instantaneous value of CHx_1MS_EPOCH. Bit 14 of CHx_CNTL (test purpose only) CNTTESTMODE bit Instantaneous value of CHx_20MS_EPOCH.
CHx_PRESET_PHASE and ALL_PRESET_PHASE Write Addresses A1, A5, A9, AD, B1, B5 and BDH
Register bit mapping Bit 7 to 0 Description Most significant bits of the Code DCO phase which is to be loaded at next TIC event if in PRESET mode.
REGISTER OPERATION In PRESET mode, the 8 bits of the PRESET_PHASE register are added to the top 7 bits of the CHx_CODE_INCR register
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GP1020
and the sum is loaded into the 8 bits of the CODE_DCO accumulator along with all zeros in the lower bits. The PRESET_PHASE register is a write only register and it can be written to at any time in PRESET mode or in UPDATE mode. The weight of the least significant bit of PRESET phase is 2p/256 radian of a half chip cycle. SHIFT_REG value GPS/ GLONASS C/A code 22 23 24 25 26 27 28 29 30 31 32 33 34 * 35 36 37 * 201 202 205 206 207 208 209 211 GLONASS GLONASS _TEST EARLY/LATE code BF3H E33H 7F6H FE3H 7F1H 3F8H BFCH A57H 72BH 395H 3CAH BE5H 7CBH 25CH B2EH 7CBH BB9H 35EH A70H 3C1H A0BH 630H AA5H 71EH 3F8H FF8H EARLY-MINUS-LATE code A12H 610H 249H 205H 621H 608H 242H A50H A52H 254H 250H 649H 648H 244H 245H 648H 222H 684H A10H 208H A08H 610H AA4H A04H 201H 610H
CHx_SHIFT_REG Read Addresses 03, 13, 23, 33, 43, 53H
Register bit mapping Bit 15 to 13 12 11 10 9 0 Description Not used; don't care data Bit 15 (MODE bit) of CHx_CNTL (test purpose only) 11th chip 12th chip First chip 10th chip
REGISTER OPERATION This register is used for test purpose only. The 12 less significant bits of the word contain the first 12-bit sequence of the C/A code issued by the channel's code generator on the dithering arm. The latching process is armed as a result of a completed slew operation, a PRESET sequence or a clock phase release by CHx_RSTB bit of the RESET_CNTL register. It is necessary to wait at least 24 Code DCO clock cycles (12 s in GPS mode and 24 s in GLONASS mode) before reading this register. The 3 most significant bits of the word are don't care data. When in Early Minus Late mode, this register will contain the first 12-bit sequence of the code sign issued on the dithering arm. The following table contains the result of the SHIFT_REG register for all possible cases. SHIFT_REG value GPS/ GLONASS C/A code 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 EARLY/LATE code F20H F90H FC8H FE4H 25BH 32DH E59H 72CH B96H B44H FA2H 7E8H BF4H FFAH FFDH 7FEH 26EH B37H 79BH 3CDH 3E6H EARLY-MINUS-LATE code 640H A40H 241H 242H 249H 24AH 248H 648H A4AH 689H 289H A82H 294H 290H 609H 229H 222H 221H 225H 228H 620H
* Note C/A Codes 34 and 37 are the same.
CHx_SIG_SEL and ALL_SIG_SEL Write Addresses 01, 11, 21, 31, 41, 51 and 71H
Register bit mapping Description Bit Signal source selection with the following encoding: Bit 3 2 1 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 x x x x 0 0 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1
Selected input port
3 to 0
0 1 2 3 4 5 6 7 8 9 Self test signal Ground Not used, don't care.
15 to 4
REGISTER DESCRIPTION CHx_SIG_SEL can be written into at any time. The SELF TEST SIGNAL is the sign and mag outputs (TSIGN and TMAG output pins) of the SELF_TEST_GENERATOR block and are wrapped round internally.
24
GP1020
CHx_TST_CODE_PHASE and ALL_TST_CODE_PHASE Write Addresses 06, 16, 26, 36, 46, 56 and 76H
This location can be written into only if the CNTTESTMODE signal, in the CHx_20MS_EPOCH is HIGH and if the MSB of the CODE_DCO phase is LOW (power up condition). The CHx_TST_CODE_PHASE is an unsigned 11 bit write only register. It is used to pre-load the CODE_PHASE counter with a specific value. ALL_TST_CODE_PHASE operates only on those channels with CNTTESTMODE set high. Register bit mapping Bit 10 to 0 Description 11 bits of the CODE_PHASE counter 15 to 5 Bit 4 to 0
CHx_1MS_EPOCH and ALL_1MS_EPOCH Write Addresses A0, A4, A8, AC, B0, B4 and BCH
These registers are write-only registers. Their operation is affected by the current channel mode, PRESET or UPDATE. In UPDATE mode, the data being written into these registers is immediately transferred to the 1 ms epoch counter. In PRESET mode however, the data is transferred only after the next TIC. Refer to section 7 of DETAILED OPERATION OF THE GP1020 for more details of the PRESET mode. Register bit mapping Description Contains the 1ms Epoch counter value to be loaded. Its valid range is from 0 to 19. Don't care
CHx_TST_CODE_SLEW Read Addresses 01, 11, 21, 31, 41, 51H
This location can be read at anytime for test purposes. It gives access to actual contents of CHx_CODE_SLEW counter. It is possible to read unstable data if the counter value is changing during the read pulse. Register bit mapping Bit 15 to 13 12 11 Don't care Bit 13 of CHx_CNTL register (test purpose only) Indicates the state of the CODE_SLEW counter (for test purpose): 0: has reached the count of zero 1: counter value is not zero and/or the counter is not enabled to count (see note) Contents of CHx_CODE_SLEW Description
CHx_20MS_EPOCH and ALL_20MS_EPOCH Write Addresses A3, A7, AB, AF, B3, B7, and BFH
These registers are write-only registers. Their operation is affected by the current channel mode, PRESET or UPDATE. In UPDATE mode, the data being written into 20MS_EPOCH is immediately transferred to the 20 ms epoch counter. In PRESET mode however, the data is transfered only after the next TIC. It is important to load the 20MS_EPOCH register last in the PRESET mode loading sequence because the trailing edge of a write to this register enables the PRESET operation on the next TIC. Refer to section 7 of DETAILED OPERATION OF THE GP1020 for more details of the PRESET mode. The CHx_20MS_EPOCH contains a test control bit (CNTTESTMODE) which is used to test different counters in the channels. When active this bit selects a 5*7 MHz clock (CLK 2) to drive the 20MS_EPOCH counter and replace the CODECLK signal by the TCK8 input signal, also TCK8 will drive the CODE GENERATOR, the CODE_SLEW and CODE_PHASE counters, and finally, it will allow the CODE GENERATOR to be set to the 1023rd chip position by a write operation to the CHx_ACCUM_RESET location and to write into the CHx_TST_CODE_PHASE and CHx_TST_CYCLE registers. Register bit mapping Bit 15 to 7 6 Not used CNTTESTMODE: Normal mode when LOW. This bit is set LOW by a master reset and should normally always be programmed LOW. When HIGH, the CODE GENERATOR, the 20MS_EPOCH, CODE_PHASE, CODE_SLEW and CARRIER_CYCLE counters are in test mode. Contains the 20 ms EPOCH counter value to be loaded. Its valid range is from 0 to 49. Description
10 to 0
NOTE : the CODE_SLEW counter is enabled to count when it has been loaded (CHx_CODE_SLEW register) and a DUMP has occured if in Update mode. In Preset mode, the counter is loaded and enabled to count upon a TIC event if the CHx_20MS_EPOCH had been loaded.
CHx_TST_CYCLE and ALL_TST_CYCLE Write Addresses 07, 17, 27, 37, 47, 57 and 77H
This location can be written into only if the CNTTESTMODE signal, in the CHx_20MS_EPOCH is active (HIGH) and if the MSB of the CARRIER_DCO phase is LOW (as at power up). The CHx_TST_CYCLE is an unsigned 16-bit write only register. It is used to pre-load the CARRIER_CYCLE counter with a specific value. The CARRIER_COUNTER is an 18-bit counter; the two Less Significant Bits will be set to 0 when writing into CHx_TST_CYCLE. ALL_TST_CYCLE operates only on those channels whose CNTTESTMODE bit is High. Register bit mapping Bit 15 to 0 Description 16 MSB bits of the CARRIER_CYCLE counter
5 to 0
DOWN_COUNT_HI and DOWN_COUNT_LO Write Addresses C3 and C4H
These two registers are used to program the Time Mark Generator. Refer to section 11 of DETAILED OPERATION OF THE GP1020 (page 31) for more details of the principle of operation of the Time Mark Generator.
25
GP1020
DOWN_COUNT_LO is programmed with a 16-bit unsigned integer word, with valid range from 0 to FFFF (HEX). DOWN_COUNT_HI is programmed with a 5-bit unsigned integer word, with valid range from 0 to 01F (HEX). The concatenated value of both registers represents the time delay, less 25 nanoseconds, from the next TIC to the Time Mark output signal in units of 50 nanoseconds. The trailing edge of a write to DOWN_COUNT_LO arms the Time Mark Generator. When the next TIC occurs, the Time Mark Counter is loaded and then decrements until it reaches zero, at which instant the Time Mark is output. by a hardware master reset. A software master reset does not affect the TIME BASE GENERATOR block, where these two flags are generated.
MEAS_STATUS_B Read Address 81H
Register bit mapping Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Description CH1_MISSED_MEAS CH2_MISSED_MEAS CH3_MISSED_MEAS CH4_MISSED_MEAS CH5_MISSED_MEAS CH6_MISSED_MEAS Not used Not used CH1_SLEW CH2_SLEW CH3_SLEW CH4_SLEW CH5_SLEW CH6_SLEW Not used Not used
MEAS_STATUS_A Read Addresses 80H
Register bit mapping Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Description CH1_NEW_MEAS_DATA CH2_NEW_MEAS_DATA CH3_NEW_MEAS_DATA CH4_NEW_MEAS_DATA CH5_NEW_MEAS_DATA CH6_NEW_MEAS_DATA Not used Not used Not used Not used Not used Not used Not used Not used MARK_FB_ACK RTC_TIC_ACK
REGISTER DESCRIPTION MEAS_STATUS_A is located at an address contiguous with accumulated data status registers so that it can be read in the same read block operation. The status bits of this register are sampled and latched on the positive edge of every INT OUT or INT IN signal. They can also be sampled and latched on request by performing a write operation to STATUS_LATCH location. BIT DESCRIPTION CHx_NEW_MEAS_DATA status bit active HIGH indicates if there is new measurement data available to be read. Each individual bit can be cleared by a write operation with don't care data to CHx_MEAS_RST. This operation releases the overwrite protection. Each bit is also cleared on the trailing edge of a read of the associated CHx_CARR_CYCLE register. If new accumulated data becomes available after status bits have been latched, the overwrite protection is not cleared while reading the CHx_CARR_CYCLE register and the CHx_NEW_MEAS_DATA bit will be set at the next MEAS_STATUS_A. A master reset (hardware or software) and the inhibition of clock phases will also clear this status bit. RTC_TIC_ACK status bit is set whenever a Real Time Clock interrupt has been received and the 100ms_TIC or 9ms_TIC following the interrupt has occured. It is reset by a read of RTC_DELAY register or an ALL_MEAS_RST command. RTC_DELAY is overwrite protected by the measurement data protection mechanism. MARK_FB_ACK status bit is set whenever a Time Mark feedback signal has been received on the selected pin, MARK_FB1, MARK_FB2 or MARK_FB3 or by the selected edge of the TIC OUT signal. It is reset by a read of PROP_DELAY_LO register or a ALL_MEAS_RST command. MARK_FB_ACK is overwrite protected by the measurement data protection mechanism. RTC_TIC_ACK and MARK_FB_ACK status bits are cleared
REGISTER DESCRIPTION MEAS_STATUS_B register is located at an address contiguous with accumulated data status registers so that it can be read in the same read block operation. The status bits of this register are sampled and latched on the positive edge of every INT OUT or INT IN signal. They can also be sampled and latched on request by performing a write operation to STATUS_LATCH location. BIT DESCRIPTION CHx_MISSED_MEAS: status bit active HIGH indicating if there has been missed measurement data resulting from a too long delay (> TIC period) before the measurement data specific to this channel was either read or the CHx_NEW_MEAS_DATA bit was cleared. This bit is set on a TIC and latched until either a master reset (hardware or software) or until a write operation to CHx_MEAS_RST CHx_SLEW: Status indicating if the code phase counter was being slewed at time of TIC sampling. If such is the case, the measurement data is not reliable. This bit is updated at each TIC when the overwrite protection is not active and is reset whenever CHx_MEAS_RST is written into with don't care data or upon a master reset (hardware or software). All status bits in this register will also be cleared when the clock phase propagation is disabled.
PROP_DELAY_LO and PROP_DELAY_HI Read Addresses C3 and C4H
Register bit mapping, PROP_DELAY_LO Bit 15 to 0 Description 16 less significant bits of down counter
Register bit mapping, PROP_DELAY_HI Bit 4 to 0 Description 5 more significant bits of down counter. Don't care, held LOW.
15 to 5
26
GP1020
PROP_DELAY_LO is a 16-bit register containing the 16 less significant bits of an unsigned integer PROP_DELAY whose value is the number, minus one, of 50 nanosecond intervals completed since the MARK output signal was generated. PROP_DELAY_HI is a 5-bit register containing the 5 more significant bits of the same integer. This integer comes from the Mark Output programmable down counter and the DOWN_COUNT register as detailed below. If a read access is performed when the programmable down counter is working the data may be not stable. A MARK_FB_ACK status bit should be acknowledged before performing a read access to the PROP_DELAY registers. The programmable down counter operates as follows: Time ta Counter contents DOWN_COUNT Remarks The counter is loaded by Software with DOWN_COUNT value. The one second time mark signal is issued and propagates through the output driver. The Down counter wraps round and continues to count down. PROP_DELAY When the feedback signal at input pin MARK FB1, MARK FB2, MARK FB3 or Internal TIC signal, as selected by bits 7 to 5 of the TIMER_CNTL register, reaches the down counter, its value is frozen and can be read by the processor, (16 lower bits only)
RESET_CNTL Read/Write Address C0H
Register bit mapping Bit 0 1 2 3 4 5 6 7 to 15 Description MRB (Chip MASTERRESET) CH1_RSTB CH2_RSTB CH3_RSTB CH4_RSTB CH5_RSTB CH6_RSTB Not used
tb
tc
BIT DESCRIPTION CHx_RSTB: When active LOW, the reset bit inhibits propagation of the clock phases to the tracking channel and resets the code generator, accumulated and measurement flags, CODE_DCO and CARRIER_DCO accumulators and their associated INCR registers, the I&D accumulators, the code slew counter and finally the code phase counter. This is required for the search algorithm of one satellite signal using many channels in order to start from a known relative code phase on all the channels. However, all of the registers in CHx can be programmed and read as usual. To restart normal operation in the different channels at the same time, the corresponding CHx_RSTB bits should be set to HIGH during the same write operation. All CHx_RSTB are set LOW by a master reset. MRB: When LOW (software reset), the effect is identical to the hardware MASTERRESET except that the clock generator and the time base generator are not affected. It should be set to HIGH to allow access to the different registers. MRB is set HIGH by a hardware master reset.
RTC_DELAY Read Address C2H
Register bit mapping Bit 15 to 0 Description Number of clock intervals counted from the occurrence of an RTC interrupt and the next TIC (TIC IN if the external source is selected). Each count represents 2.275 microsecond. The register content is unsigned and the validity range is from 0 to TIC period/2.275 microsecond.
To get the correct number of 50 ns intervals, 1 should be added to the PROP_DELAY number. For example, if the feedback was so fast that the counter did not have time to count, the PROP_DELAY value will be 1F FFFFH and by adding 1 the result becomes 00 0000H. Other examples of delay counts: PROP_DELAY value 00 0000H 00 0001H 1F FFFCH Real number of 50 ns intervals 1 2 2,097,150
If there is no feedback coming from the external driver, a timeout function will stop the counter and no MARK_FB_ACK status bit will be asserted. The PROP_DELAY value will be 1F FFFDH (representing a propagation delay of 104.8575 ms). The PROP_DELAY value can be used for: 1. Computation of DOWN_COUNT, to compensate for the propagation delay in the output driver circuit if this delay islarger than 50 nanoseconds. 2. As a BITE function, to check that the TIME_MARK output drivers work or to verify the TIC period.
The error in RTC_DELAY is 6 2.275 microsecond as shown in Fig. 16. RTC_DELAY is latched on a TIC and is overwrite protected by its own measurement data overwrite protection mechanism. The RTC_TIC_ACK status bit of MEAS_STATUS_A register indicates if an RTC interrupt has been received. The RTC_TIC_ACK status bit is cleared by writing to the ALL_MEAS_RST address and also by reading RTC_DELAY register.
27
GP1020
RTC_INT NEXT 2*275s CLOCK EDGE (FREE RUNNING) PREVIOUS 2*275s CLOCK EDGE
TIC TIME UP TO 2*275s DELAY MAKES COUNT TOO HIGH UP TO 2*275s DELAY MAKES COUNT TOO SMALL
Fig. 16
STAT_CHK_SEL Write Address C5H
Register bit mapping Description Bit Signal source selection with the following encoding: Bit 3 2 1 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 X X X X 0 0 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1
Selected input port
non valid data will be latched in STAT_CHK_SIGN and STAT_CHK_MAG registers. For this reason perform a dummy read to STAT_CHK_MAG in order to clear the flag and wait for the next time the flag is set to get valid data. NOTE: the STAT_CHK_MAG register contains the number of samples having the values 13 or23, and the STAT_CHK_SIGN register contains the number of positive samples (1 or 3) from the selected input port.
STATUS_LATCH WriteAddress 80H
0 1 2 3 4 5 6 7 8 9 Self test signal Ground A write to this location with don't care data latches the state of all status bits contained in ACCUM_STATUS_A, ACCUM_STATUS_B, MEAS_STATUS_A and MEAS_STATUS_B. Performing a write to STATUS_LATCH prior to reading the status registers ensures reading of stable status values. The latch takes effect within 200 nanoseconds of the leading edge of the write pulse. The LOW to HIGH transition of the INT signal will also latch the state of the status bit, thus it is not necessary to write to STATUS_LATCH when the status registers are to be read as a response to the INT signal in an interrupt handling routine. The write to STATUS_LATCH is required only when the status registers are read at `random' times, controlled by the microprocessor. These two mechanisms are mutually exclusive and should not be used in conjunction - if they are both used (a write to STATUS_LATCH after the occurance of an INT signal) contentions and confusion will result. To avoid this, make sure a read access does not take place at the same time as an interrupt rising edge. If the INT_MASKB bit in TIMER_CNTL register is not set to HIGH, the interrupt will not latch the status bits in the status registers ACCUM_STATUS_A, ACCUM_STATUS_B, MEAS_STATUS_A and MEAS_STATUS_B but a STATUS_LATCH write access will do so. Also, when a GP1020 is configured as a slave, it should have the INT_SOURCE and the INT_MASKB bits in the TIMER_CNTL register set to HIGH to get the status bits sampled at the same instant in both master and slave GP1020s.
3 to 0
15 to 4
Not used, don't care.
REGISTER DESCRIPTION STAT_CHK_SEL can be written into at any time. The SELF TEST SIGNAL is both the sign and magnitude outputs (TSIGN and TMAG output pins) of the SELF_TEST_GENERATOR block and are connected internally.
STAT_CHK_SIGN and STAT_CHK_MAG Read Addresses C5 and C6H
Register bit mapping Bit 13 to 0 Description Unsigned integer ranging from 0 to 16383 representing the number of sign or magnitude bits sampled during two interrupt time base periods. Don't care, held LOW.
TDATA_DUTY_CYCLE Write Address C8H
This register is associated with the SELF_TEST_GENERATOR. It allows selection of the duty cycle of the data inversion function. The time base period is 11 C/A code chips. The value of TDATA_DUTY_CYCLE, valid from 0 to 10, determines the number of chips within the time base period where the data bit modulating the self test signal will be inverted. When the self test signal is fed back in a tracking channel, the inversion causes a slope reversal in the accumulator of the Accumulate and Dump module and prevents the accumulator from saturating over a code epoch when TDATA_DUTY_CYCLE is properly set. This is the same effect as noise on a real satellite signal. REGISTER OPERATION This register is a write only register and can be written into at any time. At power up the register is reset, so it will always select the data inversion function. If the bits are all 1 the data inversion
15 to 14
These registers are overwrite protected. The overwrite protection is released and the NEW_STAT_DATA bit of the ACCUM_STATUS_A is reset on the trailing edge of a read to STAT_CHK_MAG or a write operation to ALL_ACCUM_RESET location. Therefore, STAT_CHK_MAG should be read after STAT_CHK_SIGN. For the first time the flag NEW_STAT_DATA is set after a master reset, if a write to the STAT_CHK_SEL register has not been performed within two interrupt time base (INT) periods,
28
GP1020
function will never be selected. For standard operation a single 0 is required and all the other bits must be at 1. The position of the 0 in the register allows the duty cycle of the data inversion function to be set as shown below: Bits 10 9 8 7 6 5 4 3 2 1 0 Description Register bit mapping Bit 3 Name INT_SOURCE Description When LOW, the signal used to latch the state of status bits and the results of the STAT_CHECK block is the positive edge in Intel mode or the negative edge in Motorola mode of the INT signal generated on-chip. When HIGH, the edge of the INT signal provided on INTIN pin of the device by a companion GP1020 is used instead. INT_SOURCE is set LOW by reset. When LOW, the GP1020 MARK output pin will output the time MARK output. When HIGH, the output will be driven by a signal selected by the CH1_DUMP/OSC_CHECK bit (bit 8) of this TIMER_CNTL register. TEST_OP/MARKB is set LOW by reset. Mark Feedback active edge selection, with the following encoding: Bit 765 0 0 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1 Selected function FB1 FB1 FB2 FB2 FB3 FB3 TICOUT TICOUT
0 0 0 0 0 0 0 0 0 0 0 Power up condition, the data inversion function is always selected. 1 1 1 1 1 1 1 1 1 1 0 The data inversion function is always selected. 1 1 1 1 1 1 1 1 1 0 1 The data inversion function is selected 10 times in 11. 1 1 1 1 1 1 1 1 0 1 1 The data inversion function is selected 9 times in 11.

4
TEST_OP/MARKB

0 1 1 1 1 1 1 1 1 1 1 The data inversion function is selected 1 time in 11. 1 1 1 1 1 1 1 1 1 1 1 The data inversion function is never selected.

7 to 5
TIMER_CNTL Write Address C2H
Register bit mapping Bit 0 Name TIC_PERIOD Description When LOW, the TIC period is 175 ns3571,428 = 99*9999ms. When HIGH, the TIC period is 175 ns 3 51,948 = 9*0909ms. TIC_PERIOD is set LOW by reset. When LOW, the interrupt output signal is disabled, the INT OUT pin is held LOW and the status bits are not sampled by an onchip or an externally generated interrupt. When HIGH, the interrupt output signal is enabled and the status bits will be sampled by an interrupt. INT_MASK is set LOW by reset. When LOW, TIC source is internal, when HIGH, TIC source is external (provided by a companion GP1020 through TICIN pin). TIC_SOURCE is set LOW by reset.
1
INT_MASKB
The FBx (rising edge) and FBx (falling edge) signal edges are used to calculate the pulse width of the Mark Feedback signal. This calculation allows monitoring of the pulse width and verification that the result is in accordance with the 1 ms 0.01 ms specification. The TIC OUT signal is also available as feedback for test purposes. Bits 7 to 5 are set LOW by reset.
2
TIC_SOURCE
29
GP1020
Register bit mapping Bit 8 Name CH1_DUMP/OSC _CHECK Description When LOW the GP1020 MARK output pin will output a square wave with a period of 4*55 microseconds. (40MHz/182). Because this clock is derived from the TCXO, its stability and accuracy is representative of the TCXO stability and accuracy. When HIGH, the GP1020 MARK output pin will output a square-wave changing its level at each DUMP event in channel 1. These features are used for test purposes during ATP of the GPS sensor unit and the TEST_OP/MARK bit (bit 4) must be set to HIGH to get either of these two test outputs.CH1_DUMP/ OSC_CHECK is set LOW by reset. Interrupt time base selection with the encoding given in the following table.
12 to 9
Bit 12 0 0 0 0 0 1 1 1 1 1 1 1 1
11 0 1 1 1 1 0 0 0 0 1 1 1 1
10 X 0 0 1 1 0 0 1 1 0 0 1 1
9 X 0 1 0 1 0 1 0 1 0 1 0 1
Selected interrupt timebase period (s) 505.050 420.875 505.050 589.225 673.400 757.575 841.750 925.925 1010.100 1094.275 1178.450 1262.625 1346.800
High time (s) 252.525 84.175 252.525 336.700 336.700 420.875 420.875 505.050 84.175 168.350 84.175 168.350 420.875
Low time (s) 252.525 336.700 252.525 252.525 336.700 336.700 420.875 420.875 925.925 925.925 1094.275 1094.275 925.925
Bits 12 to 9 are set LOW by reset.
30
GP1020
DETAILED OPERATION OF THE GP1020 1. MASTER RESET - Hardware or Software.
At Master Reset, all registers, accumulators and counters are cleared except CHx_CNTL. In particular, this implies the following initial states: CHx_RSTB bits of register are cleared. * Allall tracking channelthe RESET_CNTL disabled. ProgramThus clock phases are programmed in sequence with the relevant data according to the estimated DOPPLER shift. Given that the CHx_RSTB bit of the RESET_CNTL register is inactive, the programming is effective as soon as the write operation to CODE_INCR_LO is completed. If the content of CODE_INCR_HI does not need to be modified, it is not necessary to write into it. It is always necessary to write into CODE_INCR_LO in order for the programming to be effective. CODE GENERATOR PROGRAMMING 1. Select in CHx_CNTL register the type of code to be used in the dithering arm of the correlator; normally, for a search operation, either an early or a late code is selected. The PRESET/ UPDB bit will be set LOW, for example, in UPDATE mode by master reset. 2. Select in CHx_CNTL register the code to be generated among the 45 possible C/A codes or the unique GLONASS code. (Actually, all possible code combinations are programmable even those not used by the GPS constellation and some GLONASS-like codes are also available.) The selected code is applicable to both the prompt and the dithering arm. 3. Program each tracking channel CODE_SLEW register with the desired code phase. The slew operation will become effective at the first dump e.g. about 1 ms after CHx_RSTB release. The first dump will generate don't care accumulated data and will set the associated CHx_NEW_ACCUM_DATA status bit. The second and the following dumps will generate useful data. 4. Release the relevant CHx_RSTB bits of the RESET_CNTL register in order to start operation of the tracking channels. When channels of more than one GP1020 are being used to search for the same code, consecutive write operations to each chip's RESET_CNTL register should ensure a startup with reasonably well known relative code phases between the two chips. Whenever the code clock is being inhibited (to slew the code phase), the Accumulate & Dump module is held reset. It will start to accumulate correlation results only after the slew operation is completed.
* * * *
ming registers can take place either before or after releasing the CHx_RSTB bits. All the tracking channels are in UPDATE mode, the satellite code selected is GPS PRN No. 17 and the EARLY code is selected on the dithering arm. All CHx_CNTL registers are in MODE 1. The TIC generator will be free running at start-up with a 100ms TIC period setting. The INT_MASKB bit of the TIMER_CNTL register is LOW, therefore the INT_OUT signal will be disabled and the output pin held LOW. The interrupt time base is set to 505.05s. The BITECNTL bit of the BITE register is reset LOW (inactive state). The associated BITECNTL output pin is also LOW. The data bus is forced into input mode to avoid contention at power up.
2. SEARCH OPERATION at Power up, after a power glitch, or after losing satellite signals.
REGISTER INITIALISATION For each channel, the proper GPS or GLONASS signal source has to be selected by writing the proper code into CHx_SIG_SEL registers. The contents of these registers can be changed at any time during the operation to change the signal sources for any channels. At power up, all CHx_RSTB bits of the RST_CNTL register are in the reset LOW state. As stated above, in that state, all tracking channel control registers can be programmed. When it is required to perform a SEARCH for one satellite with more than one channel, these channels are first reset if not already in that state, with the corresponding CHx_RSTB bits, then the control registers are programmed. In particular, each CODE_SLEW register is programmed with a different value. Then, the CHx_RSTB bits are released, causing the channels to start operating at the same time with the same code phase. One millisecond later, all channels will get the same accumulated data and will be slewed with the pre-programmed values and will continue with a known relative code phase difference. Note that every time CHx_RSTB is set LOW, the code generator is reset. The following additional initialisation operations have to be performed. The block write addresses can be used whenever appropriate. CARRIER_DCO PROGRAMMING The CARR_INCR_HI and the CARR_INCR_LO registers are programmed in sequence with the relevant data according to the estimated DOPPLER shift for the frequency bin being looked at. The programming is effective as soon as the write operation to CARR_INCR_LO is completed (In fact, a small delay of 175 ns maximum will occur to allow synchronisation of the processor write operation to the chip operation). If the content of CARR_INCR_HI does not need to be modified, it is not necessary to write into it. It is always necessary to write into CARR_INCR_LO in order for the programming to be effective. Note that, typically, the search algorithm would dwell on a given frequency bin and perform a search over all code phases. Then it would repeat the process for the next frequency bin. CODE_DCO PROGRAMMING The tracking channel being in UPDATE mode, the PRESET_PHASE register does not need to be programmed. The CODE_INCR_HI and the CODE_INCR_LO registers are
3. READING the ACCUMULATED Data
Every time a DUMP occurs, the corresponding CHx_NEW_ACCUM_DATA status bit is set in the ACCUM_STATUS_A register. All In-phase and Quad-phase registers together with ACCUM_STATUS_A and ACCUM_STATUS_B registers are mapped in consecutive addresses so that they can be block-read after every timebase interrupt. Alternatively, a polling technique can be used by periodically reading the ACCUM_STATUS_A register to find if an interrupt or a write into STATUS_LATCH has been performed. The data contained in the IN_PHASE and QUAD_PHASE registers of the prompt and dithering arms will be protected from an overwrite due to consecutive DUMP events. The protection mechanism is released on the trailing edge of a read operation of the Q_PROMPT register. Thus the order of reading I_DITH, Q_DITH and I_PROMPT is optional but Q_PROMPT must always be read last to ensure coherence of the data set and to release the overwrite protection mechanism. The CHx_MISSED_ACCUM bit of the ACCUM_STATUS_B register indicates new accumulated data has been missed because of a too long response time for reading the accumulated data. This status bit, when set, is latched until it is cleared by a write operation to CHx_ACCUM_RESET or by a master reset or by CHx_RSTB set to LOW.
4. SEARCH on other CODE PHASES
When it is desired to correlate on the next code phase, the CODE_SLEW has to be programmed with a value of 2 (in units
31
GP1020
of half code chips). The slew will be effective on the next dump. Thus this dump will generate don't care accumulated data and as a minimum, the Q_PROMPT register will have to be read to release the overwrite protection mechanism. Note that it is only possible to delay the phase of the code. It cannot be advanced. 4. Load the following PRESET registers: PRESET_PHASE: Will set the code DCO phase. CODE_SLEW: Will set the code phase. 1MS_EPOCH: Will set the 1 ms epoch. 20MS_EPOCH:Will set the 20 ms epoch. It is important to have the PRESET mode selected prior to programming the CODE_SLEW and the EPOCH registers in order to have these new values effective on the next TIC as opposed to immediately if they were programmed under UPDATE mode.The PRESET_PHASE register can be programmed either before or after selecting the UPDATE mode. In PRESET mode the value to program in the CODE_SLEW register represents the delay between the TIC and the first code chip. To ensure correct PRESET of EPOCH counters, the loading of PRESET registers has to be completed prior to the TIC relative to which the PRESET values are computed. Thus the operation has to take place within a TIC window. It is important to load the 20MS_EPOCH register last in the loading sequence. The trailing edge of a write to this register enables the PRESET operation on the next TIC. 5. After the PRESET operation has taken place on a TIC, the PRESET/UPDB bit of the CNTL register is reset and the channel goes back to UPDATE mode. It is possible that the code phase has to be slewed so the CODE_SLEW register when loaded will then cause a slew to start on the next DUMP. On the TIC, the measurement data saved for the signal being tracked so far will be valid. The measurement data registers (or at least CHx_CARRIER_CYCLE register) must either be read or a write operation to CHx_MEAS_RESET must be made in order to clear the measurement status bits and allow measurement data acquisition on the next TIC for the new signal to be tracked under PRESET mode.
5. DATA BIT SYNCHRONISATION Related Operations
When the right code phase is found, the carrier loop is closed. The CARR_INCR_HI and CARR_INCR_LO registers can be reprogrammed at any time to close the feedback loop and resume code tracking. The Data Bit Sync algorithm should find the data bit transition instant. The processor calculates the present one millisecond epoch and programs this value into the 1MS_EPOCH register. The effect is immediate. After each DUMP, the epoch counter value can be read within 1ms and preferably at the same time as the integrate and dump registers. This provides a means of verifying that the epoch counters are indeed properly programmed. Programming the epoch counter in the 500s period following a valid CHx_NEW_ACCUM_DATA should ensure that the programming becomes effective before the next DUMP. Alternatively, the EPOCH registers can be left free-running and the delta-epoch can be added by the software each time it reads the EPOCH registers. However, the dithering between early and late code will be controlled by the actual contents of the EPOCH registers, which will not necessarily be in phase with data bit boundaries.
6. READING the MEASUREMENT Data
At every occurrence of a TIC, the measurement data is latched in measurement data registers. The TIC does not generate any interrupt signal, however, it does set the CHx_NEW_MEAS_DATA status bits of the MEAS_STATUS_A register. This register is normally always read while collecting accumulated data once every 505.05 microseconds (The INT OUT signal rate). The software tests the CHx_NEW_MEAS_DATA status bits to determine if new measurement data is available to be read. For each channel, the last measurement data register to be read must be CHx_CARR_CYCLE because the trailing edge of this read releases the overwrite protection mechanism and clears the corresponding CHx_NEW_MEAS_DATA bit. The software must also read the MEAS_STATUS_B register to determine if there was any missed measurement data or if phase and epoch counters were being slewed during the last TIC period, indicating invalid measurement data for the affected channel.
8. The TIC GENERATOR and the Interrupt Time Base
The interrupt time base consists of a free-running counter providing a pulse of constant period on a GP1020 output pin. The frequency uncertainty on this time base will be identical to the system oscillator drift. The interrupt time base shares some dividers with the TIC generator. The period of this time base is 175ns 3 2886 = 505.05s at power up, but may be changed by programming TIMER_CNTL register, and is always an exact sub-multiple of the TIC time base. Every 198th (or 18th) interrupt pulse at default rate will occur at the same time as a 100ms (or 9.0909ms) TIC, not taking into account propagation delays. Either INT IN or INT OUT (as controlled by the INT_SOURCE bit of the TIMER_CNTL register) is used to sample and latch the status bits and statistics on incoming sign and magnitude bits. The interrupt is maskable. The INT_MASKB bit of the TIMER_CNTL register when set LOW forces the logic level on the output pin to LOW. A master reset will set this bit LOW.
7. The PRESET Mode
Each tracking channel can be individually programmed to operate either in UPDATE or PRESET mode. A given channel is programmed in PRESET mode by writing a HIGH into the PRESET/UPDB bit of the CHx_CNTL register. The sequence of operations is as follows: 1. Write into CHx_CNTL to select the PRESET mode together with the appropriate code, code format on the dithering arm, etc. Since the PRESET mode is selected, the new selected code and code format will be effective on the next TIC. 2. Between the instant at which the PRESET mode is selected and the next TIC, the tracking channel will continue to operate normally, that is, it will provide accumulated data for the signal being tracked. 3. The INCRement registers of the CODE and CARRIER DCO'S have to be loaded with the appropriate frequencies for the new signal to be tracked either immediately or only after the TIC has occured if it is desired not to disturb the tracking in effect.
9. SIGNAL PATH DELAY Introduced by Hardware Signal Processing
The signal path delay has two components as follows: Dt = Total path delay = Da + Dd Da = Analogue path delay; varies with temperature and component tolerances. Dd = Digital path delay; constant if oscillator drift variations are neglected. For GPS signals, Dd = 125ns. This delay is the time from the sampling edge of the SIGN and MAG bits in the GP1010 (SAMP CLK) to the performance of the correlation in the GP1020 on these same SIGN and MAG bits (100ns) plus the delay between the correlation and the TIC clock phases in the master GP1020 (25ns).
32
GP1020
10. Short Glitch Recovery
Refer to the block diagram shown in Fig. 17 for the following discussion. It is assumed that the RTC selected provides an interrupt output signal which occurs periodically, every 100ms or every second. The interrupt is sent to both the GP1020 and the processor system. Within the GP1020, the interrupt is connected to the RTC_INT input pin of the GP1020. Its edge enables the RTC_DELAY counter. This counter is clocked by a signal with a period of 2.275s and increments until the next TIC. The TIC causes the value of RTC_DELAY to be latched in order to be read with the measurement data. If data bit synchronisation cannot be achieved on a given channel, but proper code and carrier lock are obtained, the software should jump to the data bit synchronisation algorithm. If lock is not obtained, then the software should jump to the search algorithm. Given the magnitude of error terms (summed) and the worst case error allowed in order to keep data bit synchronisation, it is possible to calculate the length of the longest permitted power glitch. See Fig. 20.
11. TIME MARK Generator
The Time Mark generator is designed to provide a one second Time Mark output signal which can be synchronised with a given time
CLOCK (439*56kHz)
REAL TIME CLOCK
RTC_INT AT 1 SEC RATE
COUNTER
ENABLE
100ms TIC RESET
MICROPROCESSOR SYSTEM
RTC_DELAY NOTES 1. Latch counter value saved on TIC. 2. Register read with measurement data.
GP1020
Fig. 17 RTC block diagram
When the processor receives the RTC interrupt, it reads the RTC time. Alternatively, RTC_TIC may not be routed to the processor, but instead, every time the RTC_TIC_ACK status bit of MEAS_STATUS_B is set in the GP1020, the software reads the RTC time. With this information, together with the contents of RTC_DELAY, the software is able to determine first the delay between the RTC and the system clock and secondly, with consecutive readings, the RTC drift can be evaluated. These two pieces of
RTC TIME READ HERE BY PROCESSOR 100ms TIC
base, such as the receiver time base, the GPS time or UTC. The Time Mark is generated after a certain programmable delay relative to the TIC. The architecture chosen (see Fig. 19) involves minimal hardware being clocked at a high rate and so gives low power consumption. As an example, to synchronise TIME MARK to UTC, the software could have the following sequence of operations (see Fig. 21):
POSITION FIX COMPUTED ON THIS TIC. TIC IS GPS TIME TAGGED.
ts
RTC_INT RTC_DELAY D
NOTES 1. D = delay between RTC timebase and system time ts. 2. Consecutive measurements of D give an indication of RTC drift. 3. Resolution of D is a function of input clock to RTC_DELAY counter.
Fig. 18 RTC timing diagram information are stored in non-volatile RAM every time they are 1. Acquire measurement data at time to (on an arbitrary TIC) calculated. After occurrence of a power glitch, the 100ms_TIC 2. Solve for UTC at measurement instant UTC (t0). Note that the timebase restarts free running but with an arbitrary phase relationsolution can only be accurate to within the hardware propaship with respect to the TICs before the power glitch. The RTC gation delays in the receiver, typically a few microseconds, interrupt process occurs again as described above and it is possible unless these delays are calibrated and UTC solution is to relate the new system TIC time relative to the previous. Ideally, this corrected accordingly. process is precise enough such that the data bit sync is not lost and 3. Compute on which 100ms TIC, tm, to take the next sample of all the channel control registers can be reprogrammed with proper measurement data such that: values. Once the timing relationship is known, the PRESET mode UTC TIME MARK 2 tm = d11d2 can be used to resume tracking of the signals.
33
GP1020
Where UTCTIME MARK = Desired time mark synchronised to a UTC second. d1 = k 3 (time between TICS), where k=INTEGER and d 1>Nav solution computation delay. d2 = time offset (with 50 ns resolution) between time mark and 100ms_TIC labelled tr d2 < (time between TICS) 4. Acquire measurement data at tm Compute Nav solution at tm Propagate Nav solution at UTC Given the oscillator drift, the delay of 25 ns added by TIME_MARK_GEN block and the calibrated propagation delay, compute DOWN_COUNT, the value to program into the programmable down counter to delay the time mark by d2. 5. Program down counter with DOWN_COUNT before the occurrence of tr. 6. Output ARINC Data within 200ms after tr (following ARINC 743) 7. Locate tm11 and go back to step 4.
40MHz MASTERCLOCK
47
CLOCK GENERATOR
4571, 428
CLK CONTROL LOGIC CNTL
20-BIT COUNTER
* * * *
100ms TIC
20-BIT PROGRAMMABLE DOWN COUNTER
EXTERNAL LINE DRIVERS MARKFBx
GP1020
1 SEC. TIME MARK
Fig. 19 Block diagram of TIME MARK generator
ts1
100ms TIC
ts2 ts3
RTC TIC
D1
D2 DRTC = (RTC22RTC12RTCDRIFT) RTC1 RTC2
NOTES 1. ts2 = ts12D11DRTC1D2 ( error terms) 2. ERROR TERMS: in ts1 in D1 in D2 : : : Equal to error terms of GPS time computation while getting the NAV solution Can be too long or too short by r, where r = RTC_DELAY counter clock period Same as D1 Residual error in RTC drift estimate, = (effective RTCDRIFT)2(estimated RTCDRIFT)
in DRTC :
Fig. 20 Timing diagram of a short glitch
COMPUTE tm NAV SOLUTION COMPUTATION DELAY 100ms TIC
d1
tm
TIME BETWEEN TICs IS CONSTANT
d2
tr
TIME OUTPUT UTC TIME MARK
t0
Fig. 21 TIME MARK timing diagram
34
GP1020
UTC ERROR BUDGET The following error budget is associated with the generation of the Time Mark: Total Error = TDOP1Clock Resolution1Oscillator Drift Residual Error. 1 Computation induced Error. 1 Time mark transfer delay through Drivers/cables. 1 Propagation delay in hardware, from antenna to correlator to measurement data sampler, where typical values are: 1. TDOP: estimated at 177ns with S/A ON (2 s number) 2. Clock Resolution: 50ns (in 21 bit programmable down counter). 3. Oscillator Drift Residual Error: (a) Due to temperature change on TCXO since last oscillator drift computation: about 50ns, computed with the following assumptions: 4. Computation induced error: It is assumed that enough significant bits are retained such that this error approximates zero. 5. TIME MARK transfer delay through drivers/cables: This will be calibrated and compensated for up to the GPS receiver's output using the feedback to the down counter. There will be a residual error due to: (a) Clock resolution = 50ns (b) Feedback delay calibration = 25ns (estimated) 6. Propagation delays in the hardware: These are estimated to be in the range of a few microseconds and are therefore the major contributor to the TIME MARK synchronisation error. An estimate could be included in the software to improve total accuracy when the total hardware design is complete. TOTAL = 177ns150ns1100ns10175ns1hardware delays TOTAL = 402ns1hardware delays.
(i) TCXO max slope is 1 ppm/C (ii) Temperature max variation is 5 C/minute (iii) The oscillator drift is computed every second and is at most one second old at UTC time mark. For example: 1ppm/C 3 5C/min 3 1sec = 83ns for a temperature step change or 41.5 ns (rounded to 50ns) for a linear ramp (b) Due to bias in drift estimation about 50ns max (rough guess)
12. INTEGRATED CARRIER PHASE measurement
The GP1020 tracking channel hardware allows measurement of integrated carrier phase through CHx_CARR_CYCLE and CHx_CARR_DCO_PHASE registers. These two registers are part of the measurement data sampled every TIC. The first one contains the 16 more significant bits of the number of full cycles elapsed and the second one contains the two remaining less significant bits plus the cycle fraction (phase). Fig. 22 shows how to add consecutive readings of these registers over several TICs in order to get a consistent integrated carrier phase.
TOTAL oscillator drift error = (a) 1 (b) 100ns.
CARRIER CYCLES MEASUREMENT OVER MORE THAN ONE TIC PERIOD
TIC0
TIC1
TIC2
Y0 2p2Y0 K1 CYCLES DY1
Y1 K2 CYCLES DY2
Y2
1. Reading at TIC0: CHx_CARR_DCO_PHASE0 = Y0 CHx_CARR_CYCLE0 CLEARED 2. Reading at TIC1: CHx_CARR_DCO_PHASE1 =Y1 CHx_CARR_CYCLE1 = K111 3. Reading at TIC2: CHx_CARR_DCO_PHASE2 = Y2 CHx_CARR_CYCLE2 = K211
DY1 = 2p(K111) 1Y12Y0 = 2p (CHx_CARR_CYCLE1)1CHx_CARR_DCO_PHASE1 2CHx_CARR_DCO_PHASE0
SDY = 2pS (CHx_CARR_CYCLE)1CHx_CARR_DCO_PHASELAST 2CHx_CARR_DCO_PHASE0
Fig. 22 Integrated carrier phase measurement
35
GP1020
13. BUILT-IN TEST Functions A. CHIP LEVEL Built-in Test Functions
SELF_TEST_GENERATOR The GP1020 provides an on-chip self-test pattern generator which is switched on under software control by setting SELF_TEST_EN bit of the BITE register. It uses tracking channel 1 or 2 according to the setting of SELF_TEST_SOURCE bit of the BITE register to generate SIGN and MAGNITUDE -like signals which can be fed back to any or all other channels by selecting the self test signal source in CHx_SIG_SEL. The selftest signal has a fixed data bit pattern of alternating one and zero every 20 milliseconds, the first bit being LOW. It has a fixed noise pattern which corresponds to particular In-phase and Quadphase accumulated values. The C/A code and the Doppler shift can be varied by programming the relevant registers of the channel which has been selected by SELF_TEST_SOURCE. The standard software can then be used to acquire and track the self-test signal but it should take into account the fact that this self-test signal is not a real GPS signal. The SELF_TEST_GENERATOR output signal can also be wrapped around externally by connecting the TSIGN and TMAG output pins to a GPS or GLONASS input port. Normally, the test source and tested channels will have the same DCO settings. The next table contains the truth table of the weight converter used in the SELF_TEST_GENERATOR : CARRIER_DCO bits (MSB-LSB) 01011 011xx 100xx 10100 All other combinations MAG 1 1 1 1 0 SIGN MSB MSB MSB MSB MSB
The design of the weight converter will drive a HIGH on the SIGN bit for 50% of the time and on the MAG bit for 31% of the time. Examples 1 and 2 show the results of the five first accumulations of the accumulated data for two different settings of the SELF_TEST_GENERATOR and the channels. Because the channels had been started at the same time, they are practically in phase with the incoming data (Sign and Mag outputs of the SELF_TEST_GENERATOR).
Example 1: Register settings BITE TDATA_DUTY_CYCLE Value (Hex) 0020 0000 Comments STG on, CH1 as source No noise (will cause an overflow condition in Q_PROMPT register if signals are in phase) Signal from the STG
CHx_SIG_SEL CHx_CODE_INCR_HI CHx_CODE_INCR_LO CHx_CARR_INCR_HI CHx_CARR_INCR_LO CHx_CNTL RESET_CNTL
000A 016E A4A8 01F5 C28F 0225 007F
SV PRN 19, Dithering code Start all channels at the same time
Results CHx_I_DITH CHx_Q_DITH CHx_I_PROMPT CHx_Q_PROMPT
First dump 0388 3D28 0A30 7FFC
Second dump 0318 3D98 093C 7FFC
Third dump 016C 3C34 0930 7FFC
Fourth dump 04CC 3D78 08F8 7FFC
Fifth dump 02AC 3FE4 0978 7FFC
36
GP1020
Example 2: Register settings BITE TDATA_DUTY_CYCLE CHx_SIG_SEL CHx_CODE_INCR_HI CHx_CODE_INCR_LO CHx_CARR_INCR_HI CHx_CARR_INCR_LO CHx_CNTL RESET_CNTL First dump 2230 0598 F8F4 46D8 Value (Hex) 0020 07F7 000A 016E A4A8 01F5 B1B3 0315 007F Second dump 1EB8 0568 0078 4798 Comments STG on, CH1 as source Invert the data 8 times in 11 Signal from the STG
SV PRN 1, Early_Minus_Late code Start all channels at the same time Third dump 2170 0374 03E8 4914 Fourth dump 2030 078C FF08 47B8 Fifth dump 1F00 03CC 0590 46D4
Results CHx_I_DITH CHx_Q_DITH CHx_I_PROMPT CHx_Q_PROMPT
ADD_DAT_TST REGISTER The ADD_DAT_TST register allows the software and the ATE to verify the functionality of the data and address busses. For full details see ADD_DAT_TST section of DETAILED DESCRIPTION OF REGISTERS.
Scan Loops and Internal Node Real-Time Observability
A number of registers are not connected to the data bus in any way. These registers have two modes of operation: The normal mode and the SCAN LOOP mode in which the flip flops are cascaded to form a shift register. There is one such scan loop per channel. Fig. 23 shows a block diagram of the Chip test functions. TDI1 (Test Data In) is a serial input common to all scan loop shift registers. Each scan loop has a separate data O/P pin TDO (1:7) (Test Data Out). The control signal TSCAN (Test Scan) determines whether the registers operate in normal mode (TSCAN LOW) or in scan loop mode (TSCAN HIGH). The Control Signal TCKS (Test Clock Select), when HIGH, selects the 7 test clocks TCK(1:7) as a replacement for the seven clock phases provided by the clock generator in normal mode. This is intended for use only in the device factory and not in normal operational use. TMS1 and TMS2 are Test Mode Select control pins. Their function is detailed in the following table: TMS2 LOW TMS1 LOW Normal mode: SIGN (2:8) and MAG (2:9) configured as inputs. TDO (1:7) held LOW. TCK(1:7) configured as inputs. SIGN (9) is always used as a normal input. Scan Loop mode: SIGN (2:8) and MAG (2:9) onfigured as inputs. TDO (1:7) output serial scan data. TCK (1:7) configured as inputs. Channel 1 observability mode: SIGN (2:8), MAG (2:9) and TCK (1:7) configured as outputs and together with TDO (1:7) allow real-time observability of internal nodes of channel 1 as listed below. The internal TIC signal and the signal latching the status bits are also available on TDO4 and TDO7 pins.
B. SYSTEM-LEVEL Built-in Test Functions
GP1010 BITE interface: The GP1020 BITE CNTL discrete output is provided to drive the corresponding discrete input pin of the GP1010. When active, this control unlocks the PLL and switches off the GP1010 frontend amplifiers. As a result, the GP1020 should read an unlocked status at its PLL LOCK discrete input. The GP1020 includes Sign and Magnitude statistics checker circuit. GLONASS IC BITE interface: Uses the same BITE CNTL discrete output to put the GLONASS IC into test mode and one GP1020 discrete input pin, GLONASSBIT, for GLONASS IC go/nogo status. TIME MARK : Three MARK FEEDBACK input pins, selected by bits 7 to 5 of TIMER_CNTL, are provided for testing the signal outputs of TIME MARK line drivers. Also, software selectable control bits (TIMER_CNTL bits 4 and 8) allow multiplexing of the normal 1 second period TIME MARK with one of two test signals, either 40MHz/91 = 439.5604KHz intended for oscillator drift measurement or CH1_DUMP for system fault-finding purposes.
LOW
HIGH
14. CHIP MANUFACTURING-TEST Functions
The GP1020 design incorporates a series of features to increase (a) the observability of internal nodes when working in the application and ( b) the observability and the controllability of the circuit during chip-level testing during manufacture. The following presents a summary of the chip test functions: TEST REGISTERS A number of registers have been added to improve the testability of the chip. They are not required for normal operation : CHx_TST_CODE_PHASE, CHx_TST_CYCLE and CHx_TST_CODE_SLEW. HIGH X
37
GP1020
SIGN (2 : 8) MAG (2 : 9)
TMS 2 TDI 1 TCK 8 TSCAN SERIAL DATA
CHANNEL 1
NODES
MUX CNTL
TDO (1)
CHANNEL 2
MUX CNTL
TDO (2)
CHANNEL 3
MUX CNTL
TDO (3)
CHANNEL 4
MUX CNTL
TDO (4)
CHANNEL 5
MUX CNTL
TDO (5)
CHANNEL 6
MUX CNTL
TDO (6)
OTHER CHIP FUNCTIONS
TMS1 CLK (1 : 7) TCKS
MUX CNTL
TDO (7)
CNTL MUX
TCK (1 : 7)
CLK (1 : 7)
CLOCK GENERATOR
Fig. 23 Chip test functions
38
GP1020
TABLE OF ACCESSIBLE CHANNEL INTERNAL NODES CNTL PIN: TMS1: CNTL PIN: SIGN9 O/P pin Prompt SIGN 2 MAG 2 SIGN 3 MAG 3 SIGN4 MAG 4 SIGN 5 bit 13 bit 11 bit 10 bit 9 bit 8 bit 7 bit 6 Dithering 13 11 10 9 8 7 6 Prompt 12 5 4 3 2 1 0 Dithering 12 5 4 3 2 1 0 LOW LOW HIGH LOW LOW HIGH LOW HIGH
IN PHASE I & Q ACCUMULATOR ARM
QUAD-PHASE I & Q ACCUMULATOR ARM Prompt MAG 5 SIGN 6 MAG 6 SIGN 7 MAG 7 SIGN 8 MAG 8 MAG 9 bit 13 bit 11 bit 10 bit 9 bit 8 bit 7 bit 6 Dump Dithering 13 11 10 9 8 7 6 Dump Prompt 12 5 4 3 2 1 0 Dump Dithering 12 5 4 3 2 1 0 Dump
MIX_CORREL output In Phase ARM Prompt TCK3 TCK4 TCK5 TCK6 CNTL PIN: TMS1: CNTL PIN: SIGN9 TDO1 TDO2 TDO3 TDO4 TDO5 TDO6 TDO7 CNTL PIN: TMS1: CNTL PIN: SIGN9 TCK1 TCK2 TCK7 Sampled SIGN Sampled MAG RESCODEGEN bit 0 bit 1 bit 2 bit 3 LOW X CodeCLK Prompt C/A code Preset load TIC CARR DCO O/P bit 27 1ms epoch carry STATUS latch control X X Dithering 0 1 2 3 Quad Phase ARM Prompt 0 1 2 3 HIGH X Code CLK Dithering C/A code CARR DCO O/P bit 25 CARR DCO O/P bit 26 CARR DCO O/P bit 27 1ms epoch carry STATUS latch control Dithering 0 1 2 3
39
GP1020
15. BOUNDARY SCAN LOOP
A boundary scan loop is implemented to allow the ATE to verify the connections of the chip at board level. The following pins are not included in Boundary Scan Loop : TDI1 PLLLOCKIN MARKFB1 NANDOP 100/219kHz SLAVECLK MARKFB2 SAMPCLK TCK(1:8) MARKFB3 MASTERCLK MARK NANDA BIAS RTCINT NANDB
The TAP controller has all functions necessary to be compatible with the JTAG standard (IEEE 1149.1-1990) with a few exceptions: All bidirectional pins are in input mode when the TRST signal is inactive (HIGH) so the chip cannot run freely when in bypass mode. state loads the instruction 000 instead of x01. *The Capture-IRTCK and TRST do not have pull-up resistors. *The pins TMS, of the pins in the loop (column by column): *This is the order A7 A8 MASTER/SLAVE TCKS MASTERRESET MOT/INTEL CS WEN RW TMS2 TMS1 TMAG* TSIGN* MAG2 INTOUT* SIGN2 MAG3 SIGN3 MAG4 SIGN4 MAG5 SIGN5 MAG6 SIGN6 MAG7 SIGN7 MAG8 SIGN8 MAG9 SIGN9 MAG1 SIGN1 MAG0 SIGN0 CLKSEL BITECNTL* GLONASSBIT INTIN TICIN TICOUT* D0 D1 D2 D3 D4 D5 D6 D7 WPROG D8 D9 D10 D11 D12 D13 D14 D15 ALE A1 A2 A3 A4 A5 A6 TSCAN
NOTE: An asterisk in the above list indicates an output pin.
40
GP1020
APPLICATION NOTES
PCB LAYOUT CONSIDERATIONS The GP1020 is a fast CMOS device so, although clock rates are low, the edge speeds can be very high. The board layout must, therefore, handle these edges on both output signals and on power supply current. SIMPLIFIED SYSTEM It is not always necessary to use all of the features of the GP1020 to make a good GPS receiver. The following pin connections show the minimum requirement and are given as a guide only. Unused inputs must be tied to VSS or VDD and not left floating. Failure to observe this may result in malfunction or damage to the device. Pin No. 1 and 2 3 4 and 5 6 7 8 9 10 11 12 13 14 and 15 16 and17 18 19 20 21 22 23 to 39 40 41 42 and 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 to 65 66 67 68 and 69 70 71 72 and 73 74 75 76 and 77 78 and 79 80 Signal name A7, A8 MASTER/SLAVE TSCAN, TCKS TDI1 MASTERRESET MOT/INTEL CS VSS VDD WEN RW TMS2, TMS1 TMAG, TSIGN MAG2 100/219kHz VDD VSS INTOUT SIGN and MAG 1 to 9 VSS VDD MAG0, SIGN0 SAMPCLK VDD MASTERCLK VSS BIAS VSS VDD VSS CLKSEL PLLLOCKIN BITECNTL GLONASSBIT SLAVECLK INTIN TCK 1to 8 TICIN TICOUT D0 and D1 VSS VDD D2 and D3 TIMEMARK RTCINT MARKFB 1 and 2 D4 and D5 VDD Description Address bus Master or Slave mode select Control Test mode Test Data serial input General reset, active low Bus mode select Chip Select, active low Ground Positive supply Write Enable - see mode table, page 3 Read/Write - see mode table, page 3 Test Mode Select 2 and 1 Test PRN pattern output Source 2 MAG input Clock output Positive supply Ground Interrupt output Source 1 to 9 SIGN and MAG inputs Ground Positive supply Source Mag and SIGN inputs Sampling clock Positive supply 40MHz Master Clock Ground Bias for Master Clock Ground Positive supply Ground 100kHz (high)/219kHz (low) select PLL Status input BITE control to Front-end GLONASS BITE input Master to Slave clock Interrupt input for Slave Test clocks or signals TIC input to Slave TIC output from Master Data bus Ground Positive supply Data bus 1 PPS output Real Time Clock interrupt input Time Mark driver feedback Data bus Positive supply Connection To microprocessor High, unless Slave Both low Low Power-on timer High for Motorola, low for Intel To microprocessor 0V 15V To microprocessor To microprocessor Both low Leave open Low Leave open 15V 0V To microprocessor All low 0V 15V To GP1010 To GP1010 15V To GP1010 0V See Fig. 12 (page 8) 0V 15V 0V High Low or GP1010 Leave open Low Leave open Low All low Low Leave open To microprocessor 0V 15V To microprocessor Leave open Low Both low To microprocessor 15V
Continued...
41
GP1020
PIN CONNECTIONS FOR A SIMPLIFIED SYSTEM (continued) Pin No. 81 82 and 83 84 85 and 86 87 88 and 89 90 91 and 92 93 94 95 96 and 97 98 and 99 100 101 102 and 103 104 to 107 108 and 109 110 111 112 and 113 114 115 to 120 Signal name VSS D6 and D7 WPROG NANDA and B TDO TCK and TRST NANDOP TMS and TDI MARKFB3 TDO7 DISCOP TDO6 and TDO5 D8 and D9 VSS VDD D10 and D11 TDO4 to TDO1 D12 and D13 VDD VSS D14 and D15 ALE A1 to A6 Description Ground Data bus Bus timing mode select Test/spare gate inputs Boundary Scan output Boundary Scan clock and Reset Test/spare gate output Boundary Scan select and input Time Mark driver feedback Test Data Output 7 General purpose output pin Test Data Outputs 6 and 5 Data bus Ground Positive supply Data bus Test Data Outputs 4 to 1 Data bus Positive supply Ground Data bus Address Latch Enable Address bus Connection 0V To microprocessor Low (see note 5) Low Leave open Both low Leave open Both low Low Leave open Leave open Leave open To microprocessor 0V 15V To microprocessor Leave open To microprocessor 15V 0V To microprocessor To microprocessor To microprocessor
Notes 1. The action of WEN and RW is given in the table at the foot of page 3. 2. In the above list, it is assumed that only one Front-end is being used and that it is connected to SIGN0 and MAG0. Any other SIGN and MAG pair may be chosen if desired. 3. Unused inputs are listed in the above table as tied low (to ground) so that they are not left floating. 4. Connections listed `To microprocessor' may, in some systems, be made via glue logic such as address latches.
5. WPROG is used to modify the Write timing. For most applications, WPROG should be tied low. For use with an Intel 486, it may be better to tie WPROG high to delay the start of the Write operation until after the address decode in the GP1020 has settled. 6. ALE is listed as `To microprocessor' but it is possible in systems with WPROG tied low to have ALE tied high to make the latches in the GP1020 transparent if the address bus is externally latched for the write or read operation.
42
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