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DS1742 Y2KC Nonvolatile Timekeeping RAM
www.maxim-ic.com
FEATURES
Integrated NV SRAM, Real-Time Clock, Crystal, Power-Fail Control Circuit and Lithium Energy Source Clock Registers are Accessed Identical to the Static RAM. These Registers are Resident in the Eight Top RAM Locations Century Byte Register Totally Nonvolatile with Over 10 Years of Operation in the Absence of Power BCD Coded Century, Year, Month, Date, Day, Hours, Minutes, and Seconds with Automatic Leap Year Compensation Valid Up to the year 2100 Battery Voltage Level Indicator Flag Power-Fail Write Protection Allows for 10% VCC Power Supply Tolerance Lithium Energy Source is Electrically Disconnected to Retain Freshness until Power is Applied for the First Time Standard JEDEC Bytewide 2k x 8 Static RAM Pinout Quartz Accuracy 1 Minute a Month at +25C, Factory Calibrated UL Recognized
PIN CONFIGURATION
TOP VIEW A7 A6 A5 A4 A3 A2 A1 A0 DQ0 DQ1 DQ2 GND 1 24 2 23 DS1742 3 22 4 21 5 20 6 19 7 18 8 17 9 16 10 15 11 14 12 13 VCC A8 A9 WE OE A10 CE DQ7 DQ6 DQ5 DQ4 DQ3
ENCAPSULATED DIP

ORDERING INFORMATION
PART DS1742-70+ DS1742-70 DS1742-100+ DS1742-100 DS1742-100IND+ DS1742-100 IND DS1742W-120+ DS1742W-150+ DS1742W-120 DS1742W-150 DS1742P-100+ VOLTAGE TEMP RANGE RANGE (V) 5.0 0C to +70C 5.0 0C to +70C 5.0 0C to +70C 5.0 0C to +70C 5.0 -40C to +85C 5.0 -40C to +85C 3.3 0C to +70C 3.3 0C to +70C 3.3 0C to +70C 3.3 0C to +70C 5.0 0C to +70C PIN-PACKAGE 28 EDIP (0.740a) 28 EDIP (0.740a) 28 EDIP (0.740a) 28 EDIP (0.740a) 28 EDIP (0.740a) 28 EDIP (0.740a) 28 EDIP (0.740a) 28 EDIP (0.740a) 28 EDIP (0.740a) 28 EDIP (0.740a) 34 PowerCap* TOP MARK DS1742-70+ DS1742-70 DS1742-100+ DS1742-100 DS1742-100IND+ DS1742-100 IND DS1742W-120+ DS1742W-150+ DS1742W-120 DS1742W-150 DS1742P-100+
*DS9034-PCX, DS9034I-PCX, DS9034-PCX+ required (must be ordered separately). A "+" indicates a lead-free product. The top mark will include a "+" symbol on lead-free devices. PowerCap is a registered trademark of Dallas Semiconductor.
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REV: 041305
DS1742
PIN DESCRIPTION
PIN 1 2 3 4 5 6 7 8 19 22 23 9 10 11 13 14 15 16 17 12 18 20 21 24 NAME A7 A6 A5 A4 A3 A2 A1 A0 A10 A9 A8 DQ0 DQ1 DQ2 DQ3 DQ4 DQ5 DQ6 DQ7 GND CE OE WE VCC FUNCTION
Address Input
Data Input/Output
Ground Active-Low Chip-Enable Input Active-Low Output-Enable Input Active-Low Write-Enable Input Power-Supply Input
DESCRIPTION
The DS1742 is a full-function, year 2000-compliant (Y2KC), real-time clock/calendar (RTC) and 2k x 8 nonvolatile static RAM. User access to all registers within the DS1742 is accomplished with a bytewide interface as shown in Figure 1. The RTC information and control bits reside in the eight uppermost RAM locations. The RTC registers contain century, year, month, date, day, hours, minutes, and seconds data in 24-hour BCD format. Corrections for the day of the month and leap year are made automatically. The RTC clock registers are double-buffered to avoid access of incorrect data that can occur during clock update cycles. The double-buffered system also prevents time loss as the timekeeping countdown continues unabated by access to time register data. The DS1742 also contains its own power-fail circuitry, which deselects the device when the VCC supply is in an out-of-tolerance condition. This feature prevents loss of data from unpredictable system operation brought on by low VCC as errant access and update cycles are avoided.
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DS1742
CLOCK OPERATIONS--READING THE CLOCK
While the double-buffered register structure reduces the chance of reading incorrect data, internal updates to the DS1742 clock registers should be halted before clock data is read to prevent reading of data in transition. However, halting the internal clock register updating process does not affect clock accuracy. Updating is halted when a 1 is written into the read bit, bit 6 of the century register, see Table 2. As long as a 1 remains in that position, updating is halted. After a halt is issued, the registers reflect the count, that is day, date, and time that was current at the moment the halt command was issued. However, the internal clock registers of the double-buffered system continue to update so that the clock accuracy is not affected by the access of data. All of the DS1742 registers are updated simultaneously after the internal clock register updating process has been re-enabled. Updating is within a second after the read bit is written to 0. The READ bit must be a zero for a minimum of 500ms to ensure the external registers will be updated. Figure 1. DS1742 BLOCK DIAGRAM
Table 1. TRUTH TABLE VCC CE VIH VIL VCC > VPF VIL VIL VSO < VCC < VPF X VCC < VSO < VPF X
OE
WE
X X VIL VIH X X
X VIL VIH VIH X X
MODE Deselect Write Read Read Deselect Deselect
DQ High-Z Data In Data Out High-Z High-Z High-Z
POWER Standby Active Active Active CMOS Standby Data Retention Mode
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DS1742
SETTING THE CLOCK
As shown in Table 2, bit 7 of the century register is the write bit. Setting the write bit to a 1, like the read bit, halts updates to the DS1742 registers. The user can then load them with the correct day, date and time data in 24-hour BCD format. Resetting the write bit to a 0 then transfers those values to the actual clock counters and allows normal operation to resume.
STOPPING AND STARTING THE CLOCK OSCILLATOR
The clock oscillator may be stopped at any time. To increase the shelf life, the oscillator can be turned off to minimize current drain from the battery. The OSC bit is the MSB (bit 7) of the seconds registers, see Table 2. Setting it to a 1 stops the oscillator.
FREQUENCY TEST BIT
As shown in Table 2, bit 6 of the day byte is the frequency test bit. When the frequency test bit is set to logic 1 and the oscillator is running, the LSB of the seconds register will toggle at 512 Hz. When the seconds register is being read, the DQ0 line will toggle at the 512 Hz frequency as long as conditions for access remain valid (i.e., CE low, OE low, WE high, and address for seconds register remain valid and stable).
CLOCK ACCURACY
The DS1742 is guaranteed to keep time accuracy to within 1 minute per month at 25C. Dallas Semiconductor calibrates the RTC at the factory using nonvolatile tuning elements. The DS1742 does not require additional calibration. For this reason, methods of field clock calibration are not available and not necessary. Clock accuracy is also affected by the electrical environment and caution should be taken to place the RTC in the lowest level EMI section of the PCB layout. For additional information refer to Application Note 58. Table 2. REGISTER MAP
ADDRESS 7FF 7FE 7FD 7FC 7FB 7FA 7F9 7F8
W = WRITE BIT
B7 X X BF X X
OSC
B6 X
B5 10 Year X
DATA B4 B3
B2 B1 Year Month
B0
FUNCTION Year Month Date Day Hour Minutes Seconds Control
RANGE 00-99 01-12 01-31 01-07 00-23 00-59 00-59 00-39
W
10 Month X 10 Date FT X X X 10 Hour 10 Minutes 10 Seconds R 10 Century
R = READ BIT X = SEE NOTE BELOW
X
Date Day Hour Minutes Seconds Century
OSC = STOP BIT
FT = FREQUENCY TEST BF = BATTERY FLAG
Note: All indicated "X" bits are not used but must be set to "0" during write cycle to ensure proper clock operation.
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DS1742
RETRIEVING DATA FROM RAM OR CLOCK
The DS1742 is in the read mode whenever OE (output enable) is low, WE (write enable) is high, and CE (chip enable) is low. The device architecture allows ripple-through access to any of the address locations in the NV SRAM. Valid data will be available at the DQ pins within tAA after the last address input is stable, providing that the CE , and OE access times and states are satisfied. If CE , or OE access times and states are not met, valid data will be available at the latter of chip enable access (tCEA) or at output enable access time (tOEA). The state of the data input/output pins (DQ) is controlled by CE , and OE . If the outputs are activated before tAA, the data lines are driven to an intermediate state until tAA. If the address inputs are changed while CE , and OE remain valid, output data will remain valid for output data hold time (tOH) but will then go indeterminate until the next address access.
WRITING DATA TO RAM OR CLOCK
The DS1742 is in the write mode whenever WE , and CE are in their active state. The start of a write is referenced to the latter occurring transition of WE , on CE . The addresses must be held valid throughout the cycle. CE or WE must return inactive for a minimum of tWR prior to the initiation of another read or write cycle. Data in must be valid tDS prior to the end of write and remain valid for tDH afterward. In a typical application, the OE signal will be high during a write cycle. However, OE can be active provided that care is taken with the data bus to avoid bus contention. If OE is low prior to WE transitioning low the data bus can become active with read data defined by the address inputs. A low transition on WE will then disable the outputs tWEZ after WE goes active.
DATA RETENTION MODE
The 5V device is fully accessible and data can be written or read only when VCC is greater than VPF. However, when VCC is below the power fail point, VPF, (point at which write protection occurs) the internal clock registers and SRAM are blocked from any access. When VCC falls below the battery switch point VSO (battery supply level), device power is switched from the VCC pin to the backup battery. RTC operation and SRAM data are maintained from the battery until VCC is returned to nominal levels. The 3.3V device is fully accessible and data can be written or read only when VCC is greater than VPF. When VCC falls below the power fail point, VPF, access to the device is inhibited. If VPF is less than Vso, the device power is switched from VCC to the backup supply (VBAT) when VCC drops below VPF. If VPF is greater than Vso, the device power is switched from VCC to the backup supply (VBAT) when VCC drops below Vso. RTC operation and SRAM data are maintained from the battery until VCC is returned to nominal levels.
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DS1742
BATTERY LONGEVITY
The DS1742 has a lithium power source that is designed to provide energy for clock activity, and clock and RAM data retention when the VCC supply is not present. The capability of this internal power supply is sufficient to power the DS1742 continuously for the life of the equipment in which it is installed. For specification purposes, the life expectancy is 10 years at 25C with the internal clock oscillator running in the absence of VCC power. Each DS1742 is shipped from Dallas Semiconductor with its lithium energy source disconnected, guaranteeing full energy capacity. When VCC is first applied at a level greater than VPF, the lithium energy source is enabled for battery backup operation. Actual life expectancy of the DS1742 will be much longer than 10 years since no lithium battery energy is consumed when VCC is present.
BATTERY MONITOR
The DS1742 constantly monitors the battery voltage of the internal battery. The Battery Flag bit (bit 7) of the day register is used to indicate the voltage level range of the battery. This bit is not writable and should always be a 1 when read. If a 0 is ever present, an exhausted lithium energy source is indicated and both the contents of the RTC and RAM are questionable.
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DS1742
ABSOLUTE MAXIMUM RATINGS
Voltage Range on Any Pin Relative to Ground.....................................................-0.3V to +6.0V Operating Temperature Range......................................................0C to +70C (noncondensing) Storage Temperature Range...........................................................................-40C to +85C Soldering Temperature.................................See IPC/JEDEC J-STD-020 Specification (See Note 7)
This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.
OPERATING RANGE
RANGE Commercial Industrial TEMPERATURE 0C to +70C (noncondensing) -40C to +85C (noncondensing) VCC 3.3V 10% or 5V 10% 3.3V 10% or 5V 10%
RECOMMENDED DC OPERATING CONDITIONS (Over the operating range)
PARAMETER Logic 1 Voltage (All Inputs) Logic 0 Voltage (All Inputs) VCC = 5V 10% VCC = 3.3V 10% VCC = 5V 10% VCC = 3.3V 10% SYMBOL VIH VIH VIL VIL MIN 2.2 2.0 -0.3 -0.3 TYP MAX VCC + 0.3V VCC + 0.3V +0.8 +0.6 UNITS V V V V NOTES 1 1 1 1
DC ELECTRICAL CHARACTERISTICS
(VCC = 5.0V 10%, Over the operating range.) PARAMETER SYMBOL Active Supply Current TTL Standby Current ( CE = VIH) CMOS Standby Current ( CE VCC - 0.2V) Input Leakage Current (Any Input) Output Leakage Current (Any Output) Output Logic 1 Voltage (IOUT = -1.0mA) Output Logic 0 Voltage (IOUT = +2.1mA) Write Protection Voltage Battery Switchover Voltage ICC ICC1 ICC2 IIL IOL VOH VOL VPF VSO 4.25 VBAT -1 -1 2.4 0.4 4.50 V MIN TYP 15 1 1 MAX 50 3 3 +1 +1 UNITS mA mA mA mA mA 1 1 1 1, 4 NOTES 2, 3 2, 3 2, 3
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DS1742
DC ELECTRICAL CHARACTERISTICS
(VCC = 3.3V 10%, Over the operating range.) PARAMETER SYMBOL MIN Active Supply Current TTL Standby Current ( CE = VIH) CMOS Standby Current ( CE VCC - 0.2V) Input Leakage Current (any input) Output Leakage Current (Any Output) Output Logic 1 Voltage (IOUT = -1.0mA) Output Logic 0 Voltage (IOUT =2.1mA) Write Protection Voltage Battery Switchover Voltage ICC ICC1 ICC2 IIL IOL VOH VOL VPF VSO 2.80 VBAT or VPF -1 -1 2.4 0.4 2.97 V V TYP 10 0.7 0.7 MAX 30 2 2 +1 +1 UNITS mA mA mA mA mA 1 1 1 1, 4 NOTES 2, 3 2, 3 2, 3
AC CHARACTERISTICS--READ CYCLE (5V)
(VCC = 5.0V 10%, Over the operating range.) 70ns ACCESS PARAMETER SYMBOL MIN MAX Read Cycle Time tRC 70 Address Access Time tAA 70 5 tCEL CE to DQ Low-Z tCEA 70 CE Access Time 25 tCEZ CE Data Off time tOEL 5 OE to DQ Low-Z tOEA 35 OE Access Time tOEZ 25 OE Data Off Time Output Hold from Address tOH 5 100ns ACCESS MIN MAX 100 100 5 100 35 5 55 35 5 UNITS ns ns ns ns ns ns ns ns ns NOTES
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DS1742
AC CHARACTERISTICS--READ CYCLE (3.3V)
(VCC = 3.3V 10%, Over the operating range.) 120ns ACCESS PARAMETER SYMBOL MIN MAX Read Cycle Time tRC 120 Address Access Time tAA 120 tCEL 5 CE to DQ Low-Z tCEA 120 CE Access Time tCEZ 40 CE Data Off time tOEL 5 OE to DQ Low-Z tOEA 100 OE Access Time 35 tOEZ OE Data Off Time Output Hold from Address tOH 5 150ns ACCESS MIN MAX 150 150 5 150 50 5 130 35 5 UNITS ns ns ns ns ns ns ns ns ns NOTES 5 5 5 5 5 5 5 5 5
READ CYCLE TIMING DIAGRAM
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DS1742
AC CHARACTERISTICS--WRITE CYCLE (5V)
(VCC = 5.0V 10%, Over the operating range.) 70ns ACCESS PARAMETER SYMBOL MIN MAX Write Cycle Time tWC 70 Address Access Time tAS 0 tWEW 50 WE Pulse Width tCEW 60 CE Pulse Width Data Setup Time tDS 30 Data Hold time tDH 0 Address Hold Time tAH 5 tWEZ 25 WE Data Off Time Write Recovery Time tWR 5 100ns ACCESS MIN MAX 100 0 70 75 40 0 5 35 5 UNITS NOTES ns ns ns ns ns ns ns ns ns
AC CHARACTERISTICS--WRITE CYCLE (3.3V)
(VCC = 3.3V 10%, Over the operating range.) 120ns ACCESS PARAMETER SYMBOL MIN MAX Write Cycle Time tWC 120 Address Setup Time tAS 0 100 tWEW WE Pulse Width tCEW 110 CE Pulse Width Data Setup Time tDS 80 Data Hold Time tDH 0 Address Hold Time tAH 0 40 tWEZ WE Data Off Time Write Recovery Time tWR 10 150ns ACCESS MIN MAX 150 0 130 140 90 0 0 50 10 UNITS NOTES ns ns ns ns ns ns ns ns ns
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DS1742
WRITE CYCLE TIMING DIAGRAM--WRITE-ENABLE CONTROLLED
WRITE CYCLE TIMING DIAGRAM--CHIP-ENABLE CONTROLLED
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DS1742
POWER-UP/POWER-DOWN CHARACTERISTICS (5V)
(VCC = 5.0V 10%, Over the operating range.) PARAMETER
CE
SYMBOL tPD tF tFB tR tREC tDR
MIN 0 300 10 0
TYP
MAX
UNITS ms ms ms ms
NOTES
or WE at VIH, Before Power-Down
VCC Fall Time: VPF(MAX) to VPF(MIN) VCC Fall Time: VPF(MIN) to VSO VCC Rise Time: VPF(MIN) to VPF(MAX) Power-Up Recover Time Expected Data Retention Time (Oscillator On)
35 10
ms years 5, 6
POWER-UP/POWER-DOWN WAVEFORM TIMING (5V DEVICE)
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DS1742
POWER-UP/POWER-DOWN CHARACTERISTICS (3.3V)
(VCC = 3.3V 10%, Over the operating range.) PARAMETER
CE
SYMBOL tPD tF tR tREC tDR
MIN 0 300 0
TYP
MAX
UNITS ms ms ms
NOTES
or WE at VIH, Before Power-Down
VCC Fall Time: VPF(MAX) to VPF(MIN) VCC Rise Time: VPF(MIN) to VPF(MAX) Power-Up Recovery Time Expected Data Retention Time (Oscillator On)
35 10
ms years 5, 6
POWER-UP/POWER-DOWN WAVEFORM TIMING (3.3V DEVICE)
CAPACITANCE
(TA = +25C) PARAMETER Capacitance on All Input Pins Capacitance on All Output Pins SYMBOL CIN CO MIN TYP MAX 7 10 UNITS pF pF NOTES
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DS1742
AC TEST CONDITIONS
Output Load: 100pF + 1TTL Gate Input Pulse Levels: 0.0 to 3.0V Timing Measurement Reference Levels: Input: 1.5V Output: 1.5V Input Pulse Rise and Fall Times: 5ns
NOTES:
1) Voltage referenced to ground. 2) Typical values are at 25C and nominal supplies. 3) Outputs are open. 4) Battery switchover occurs at the lower of either the battery voltage or VPF. 5) Data retention time is at 25C. 6) Each DS1742 has a built-in switch that disconnects the lithium source until VCC is first applied by the user. The expected tDR is defined as a cumulative time in the absence of VCC starting from the time power is first applied by the user. 7) Real-time clock modules can be successfully processed through conventional wave-soldering techniques as long as temperature exposure to the lithium energy source contained within does not exceed +85C. Post-solder cleaning with water washing techniques is acceptable, provided that ultrasonic vibration is not used to prevent damage to the crystal.
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DS1742
PACKAGE INFORMATION
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo.)
DS1742 24-PIN PACKAGE
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Maxim/Dallas Semiconductor cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim/Dallas Semiconductor product. No circuit patent licenses are implied. Maxim/Dallas Semiconductor reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
(c) 2005 Maxim Integrated Products * Printed USA
The Maxim logo is a registered trademark of Maxim Integrated Products, Inc. The Dallas logo is a registered trademark of Dallas Semiconductor Corporation.

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