 |
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
| Datasheet File OCR Text: |
| AN106 Application Note QUICK CS6420 SPEAKERPHONE INTERFACE This application note describes a quick interface for the Crystal Semiconductor CS6420 speakerphone device to an existing analog speakerphone. The electrical connections to the speakerphone take advantage of standard signals present in all analog speakerphones. Connections are made to the Tip and Ring of an analog telephone line and the CS6420 uses the speakerphone's speaker and microphone for its acoustic interface. Figure 1 illustrates the system connections. Minor modifications are made to the speakerphone to gain access to certain signals and wires. Six signals are connected between the target speakerphone and the CS6420 circuit card. The phone's speaker and microphone wires are disconnected from the speakerphone's circuitry and brought to the CS6420 circuit card. This provides the CS6420's acoustic interface and accounts for four of the six signals (SPKR+, SPKR-, MIC+ and MIC-). With the CS6420 connected to the speaker and microphone, hands-free full duplex operation and speaker volume control are available. The Tip and Ring signals in the speakerphone are not disconnected from the speakerphone's circuitry. The connections are made in parallel keeping the speakerphone's keypad functional. ANALOG TELEPHONE LINE AC WALL ADAPTER SPEAKER TIP AND RING TELEPHONE SPEECH NETWORK 5V POWER Volume Control CS6420 C UP DOWN MICROPHONE CRD6420 CIRCUIT CARD Figure 1. Speakerphone System Connections Cirrus Logic, Inc. Crystal Semiconductor Products Division P.O. Box 17847, Austin, Texas 78760 (512) 445 7222 FAX: (512) 445 7581 http://www.crystal.com Copyright (c) Cirrus Logic, Inc. 1998 (All Rights Reserved) FEB `98 AN106Rev1 1 AN106 This configuration permits easy evaluation of hands-free communication with a full duplex speakerphone. The speaker and microphone are housed in an actual chassis, providing a realistic environment. Various speakerphone designs can be quickly tested since standard analog signals are passed between the speakerphone and CS6420 circuit card. This method also uses the speakerphone's (tone) dialer. Note that the performance of this system is dependent on the speakerphone used. In general the design criteria for full duplex speakerphones is much more stringent than for half duplex phones. In particular, distortion performance and acoustic coupling control are critical to good full duplex design. It is relatively easy to get the modified half-duplex speakerphone to work in full-duplex; however, its performance may suffer, particularly in near-end speaker volume and in idle channel noise in the transmit direction. Additionally, any distortion introduced by the speaker or the phone housing will result in uncancelled echo perceived at the far end. The CS6420 circuit card interfaces to the telephone network via the Tip and Ring signals of the analog telephone line. The Tip and Ring signals are routed to a telephone speech network which converts the 2-wire analog telephone signal to 4-wire transmit and receive signals. The receive and transmit signals are interfaced to the CS6420's Network In (NI) and Network Out (NO) ports, respectively. The circuit for the POTS (Plain Old Telephone Service) analog telephone line interface is shown in Figure 2. The 2-to-4 wire telephone hybrid is implemented with a Motorola MC34014. The MC34014 (U5) is a standard speech network meant for connection to the Tip and Ring lines through a polarity bridge (D6-D9). The discrete components surrounding U5 are as suggested by the MC34014 data sheet. The components which set the dc voltage characteristics have been omitted since this is established by the speech network in the speakerphone. (Recall that the speakerphone's Tip and Ring signals remain connected to the POTS line in order to utilize the phone's keypad.) The omitted components include a resistor connected to LR (U5-13) and a capacitor connected to LC (U5-12). Connection to the analog telephone line is made through J1, which is an RJ11 receptacle. This receptacle is a standard telephone connector that connects to the typical telephone cable provided with telephones. A DPDT switch (S1) is used to switch between ON HOOK and OFF HOOK. The transmit and receive signals from the MC34014 are buffered and AC coupled using a Motorola op-amp MC33078 (U3). The gain of the op-amp circuit is set such that the NI amplitude is within the CS6420's limits of 1 Vrms and the CS6420's NO signal level, also 1 Vrms, adjusted to meet the MC34014's TX requirements. R9 and R10 create a voltage divider that establishes a voltage to bias the op-amp's inputs at 2.5 volts. The schematic for the CS6420 (U1) circuitry is shown in Figure 3. The circuitry is identical to the typical connections described in the CS6420 data sheet and incorporated on the CDB6420 evaluation board. Figures 4 and 5 are schematics for the speaker driver and microphone bias respectively. The Motorola MC34119 (U2) provides the capability to drive speaker loads down to 8 ohms. The microphone bias circuitry provides the necessary constant current source for an electret microphone. Both of these circuits are used on the CDB6420 evaluation board and are described in the CDB6420 data sheet. A microcontroller is interfaced to the CS6420 to adjust the default settings and control speaker volume. Figure 6 contains a schematic using the Microchip PIC16C84 (U4) microcontroller. U4 writes control words to the CS6420's four control registers using a 3-wire interface (DRDY, STROBE, AN106Rev1 2 AN106 Figure 2. Interface to the Tip and Ring Signals of a POTS Line AN106Rev1 3 AN106 Figure 3. CS6420 Connection Diagram Figure 4. Speaker Driver Circuit 4 AN106Rev1 AN106 and DATA). The microcontroller reads one of the two momentary switches that provide signals to either increase or decrease the speaker volume. The input signals are deciphered, and the volume control word is sent to the CS6420. The digital interface and control words are described in the CS6420 data sheet. The assembly code for the PIC16C84 is provided at the end of this application note. Figure 7 illustrates the power supply circuitry. The circuitry is designed to use a common +6 V DC power supply. The supply used should be able to source a minimum of 200mA. A diode (D5) provides a diode drop to reduce the voltage to around 5 volts. Z1 is a zener diode added to provide overvoltage and polarity inversion protection. For noise performance, the 5 volt digital voltage (+5 VD) is filtered using a ferrite bead. Figure 5. Microphone Bias Circuit Figure 6. Microcontroller Interface Circuit AN106Rev1 5 AN106 Figure 7. Power Supply Circuitry and Phone Connection Pinout 6 AN106Rev1 AN106 PIC16C84 ASSEMBLY CODE ;*************************************************************************** ;* ;* File: crd6420.asm ;* Date: May 12, 1997 ;* ;* PIC16C84 ;* ;* Program entry point is at routine "Main". The entry point ;* is address 0x05 ;*************************************************************************** ;* ;* Program is designed to provide simple volume control for the CS6420 ;* in a CDB6420-based demo. Two buttons, one to increase volume and ;* one to decrease volume are connected to PortB of the PIC16C84. Four ;* PortA pins are used to control the CS6420's Microcontroller Interface. ;* ;*************************************************************************** ;******** Memory Map Equates INDF equ 0x00 ; Indirect Address Register STATUS equ 0x03 ; STATUS register equate RP0 equ 0x05 ; Register Bank Select Bit ZERO equ 0x02 ; Represents the Zero Bit in Status Reg CARRY equ 0x00 ; Represents the Carry Bit in Status Reg FSR equ 0x04 ; File Select Register PORTA equ 0x05 ; General Purpose I/O Port PORTB equ 0x06 ; General Purpose I/O Port INTCON equ 0x0B ; INTCON register equate GIE equ 0x07 ; Represents the GIE bit in IntCon Reg RBIE equ 0x03 ; Represents the RBIE bit in IntCon Reg RBIF equ 0x00 ; Represents the RBIF bit in IntCon Reg OPT_REG equ 0x81 ; OPTION register equate RBPU equ 0x07 ; Represents the RBPU bit in Option Reg TRISA equ 0x85 ; Data Direction Control For Port A TRISB equ 0x86 ; Data Direction Control For Port B DATAIN equ 0x00 ; Port A bit 0 STROBE equ 0x01 ; Port A bit 1 DRDY equ 0x02 ; Port A bit 2 RST equ 0x03 ; Port A bit 3 INC equ 0x04 ; Port B bit 4 DEC equ 0x05 ; Port B bit 5 ;******** Ram Memory Equates Reg0Hi equ Reg1Hi equ Reg2Hi equ Reg3Hi equ Reg0Lo equ Reg1Lo equ Reg2Lo equ Reg3Lo equ RegHi equ RegLo equ Temp equ RVol equ Count equ Port equ DelayTime equ DelayMore equ 0x0C 0x0D 0x0E 0x0F 0x10 0x11 0x12 0x13 0x14 0x15 0x16 0x17 0x18 0x19 0x1a 0x1b ; Upper 8 bits of Reg0 ; Upper 8 bits of Reg1 ; Upper 8 bits of Reg2 ; Upper 8 bits of Reg3 ; Lower 8 bits of Reg0 ; Lower 8 bits of Reg1 ; Lower 8 bits of Reg2 ; Lower 8 bits of Reg3 ; Upper 8 bits of Transmit Reg ; Lower 8 bits of Transmit Reg ; Temporary byte ; Volume control variable ; Loop counter ; PortB temporary value ; Delay counter ; Delay counter AN106Rev1 7 AN106 ;*************************************************************************** ;* Program Code ;*************************************************************************** processor 16C84 ; Set Processor Type org 0x00 ; Reset Vector goto Main ; Start at Main org 0x04 ; Interrupt Vector goto ISR ; Service the Interrupt ;*************************************************************************** ;* ;* Routine - Main ;* Input - none ;* Output - none ;* This is the entry point to the program ;*************************************************************************** org 0x05 Main ; Start from Reset Vector ;******** Initialize System and Perform SELF OFFSET Calibration CALL Initialization ; Initialize the system CALL PowerOn ; Powerup the CS6420 Here GOTO Here ; Infinite loop 8 AN106Rev1 AN106 ;*************************************************************************** ;* ;* Routine - Initialization ;* Input - none ;* Output - none ;* Set up default control bytes, default volume setting, port pins ;*************************************************************************** Initialization ; Set up default control bytes ;This configuration has the microphone tied directly to APO. ; Reg0Hi MOVLW 0x20 ;mic preamp off, RVol = +24 dB, TGain = +12 dB MOVWF Reg0Hi ; Reg0Lo MOVLW 0x58 MOVWF Reg0Lo ; Reg1Hi MOVLW 0x20 ;TVol = +21 dB, RGain = +12 dB MOVWF Reg1Hi ; Reg1Lo MOVLW 0x7a MOVWF Reg1Lo ; Reg2Hi MOVLW 0x08 ;RHDet = 6 dB, RSThd = 6 dB, PCSen = low MOVWF Reg2Hi ; Reg2Lo MOVLW 0x2c MOVWF Reg2Lo ; Reg3Hi MOVLW 0x0a ;THDet = 6 dB, TSAtt = 24 dB MOVWF Reg3Hi ; Reg3Lo MOVLW 0x0b MOVWF Reg3Lo ; Set up default volume setting ; RVol = 0x02 (24 dB) (max of 0x1f) MOVLW 0x02 MOVWF RVol ; Set up port pins ; 2 inputs (increase volume, decrease volume) ; 4 outputs (/RST, /DRDY, STROBE, DATAIN) CLRF PORTA ; Initialize PORTA by setting output ; data latches. CLRF PORTB ; Initialize PORTB by setting output ; data latches. BSF STATUS, RP0 ; Select Bank 1 MOVLW 0x00 ; Value used to initialize direction MOVWF TRISA ; Set PortA as outputs MOVLW MOVWF BCF BCF MOVLW MOVWF MOVLW MOVWF BSF BSF RETURN 0x30 TRISB OPT_REG,RBPU STATUS, RP0 0xff PORTA 0x0f PORTB INTCON,RBIE INTCON,GIE ; Value used to initialize direction ; Set PortB RB5 and RB4 as inputs ; Enable weak pullups on PortB ; Select Bank 0 ; bring all port pins high ; bring all port pins high ; Enable interrupt on PortB change ; Enable all interrupts AN106Rev1 9 AN106 ;*************************************************************************** ;* ;* Routine - Power On ;* Input - none ;* Output - RegXHi,RegXLo ;* Reset CS6420 and initialize registers ;*************************************************************************** PowerOn BCF PORTA,RST ; bring /RST lo BSF PORTA,RST ; bring /RST hi ; Write Reg0 (RegHi=Reg0Hi, RegLo=Reg0Lo) CALL Delay ; hold time MOVF Reg0Hi,0 ; move Reg0Hi to W MOVWF RegHi ; move W to RegHi MOVF Reg0Lo,0 ; move Reg0Lo to W MOVWF RegLo ; move W to RegLo CALL WriteReg ; Write Reg1 (RegHi=Reg1Hi, RegLo=Reg1Lo) MOVF Reg1Hi,0 ; move Reg1Hi to W MOVWF RegHi ; move W to RegHi MOVF Reg1Lo,0 ; move Reg1Lo to W MOVWF RegLo ; move W to RegLo CALL WriteReg ; Write Reg2 (RegHi=Reg2Hi, RegLo=Reg2Lo) MOVF Reg2Hi,0 ; move Reg2Hi to W MOVWF RegHi ; move W to RegHi MOVF Reg2Lo,0 ; move Reg2Lo to W MOVWF RegLo ; move W to RegLo CALL WriteReg ; Write Reg3 (RegHi=Reg3Hi, RegLo=Reg3Lo) MOVF Reg3Hi,0 ; move Reg3Hi to W MOVWF RegHi ; move W to RegHi MOVF Reg3Lo,0 ; move Reg3Lo to W MOVWF RegLo ; move W to RegLo CALL WriteReg CALL UpdateRVol ; Update RVol RETURN ;*************************************************************************** ;* ;* Routine - ISR ;* Input - none ;* Output - none ;* The ISR calls IncreaseVolume or DecreaseVolume as appropriate ;*************************************************************************** ISR MOVF PORTB,0 ; move contents of PortB to W MOVWF Port ; save contents to Temp for bit test BTFSS Port,INC ; if INC is high, is DEC set? CALL IncreaseVolume ; else IncreaseVolume BTFSS Port,DEC ; if DEC is high, fail CALL DecreaseVolume ; else DecreaseVolume BCF INTCON, RBIF ; clear port interrupt RETFIE ; return from interrupt 10 AN106Rev1 AN106 ;*************************************************************************** ;* ;* Routine - Increase Volume ;* Input - none ;* Output - RVol ;* If RVol>0x00 increment RVol and update ;*************************************************************************** IncreaseVolume MOVF RVol,0 ; move RVol to W SUBLW 0x00 ; W = 0x00 - RVol BTFSS STATUS,ZERO ; if zero bit is set, don't decrement DECF RVol ; else decrement CALL UpdateRVol ; Update RVol RETURN ;*************************************************************************** ;* ;* Routine - Decrease Volume ;* Input - none ;* Output - RVol ;* If RVol<0x1f increment RVol and update ;*************************************************************************** DecreaseVolume MOVF RVol,0 ; move RVol to W SUBLW 0x1f ; W = 0x1f - RVol BTFSS STATUS,ZERO ; if zero bit is set, don't increment INCF RVol ; else increment CALL UpdateRVol ; Update RVol RETURN ;*************************************************************************** ;* ;* Routine - Update RVol ;* Input - Move RVol to Reg0Hi:Reg0Lo ;* Output - Reg0Hi,Reg0Lo ;* This routine takes RVol and updates Reg0 with the values ;*************************************************************************** UpdateRVol BCF Reg0Hi,1 BCF Reg0Hi,0 BCF Reg0Lo,7 BCF Reg0Lo,6 BCF Reg0Lo,5 ; set RVol area in Reg0 to 0s BTFSC RVol,4 BSF Reg0Hi,1 ; set appropriate bit to 1 as needed BTFSC RVol,3 BSF Reg0Hi,0 BTFSC RVol,2 BSF Reg0Lo,7 BTFSC RVol,1 BSF Reg0Lo,6 BTFSC RVol,0 BSF Reg0Lo,5 MOVF Reg0Hi,0 ; move Reg0Hi to W MOVWF RegHi ; move W to RegHi MOVF Reg0Lo,0 ; move Reg0Lo to W MOVWF RegLo ; move W to RegLo CALL WriteReg RETURN AN106Rev1 11 AN106 ;*************************************************************************** ;* ;* Routine - WriteReg (keeps /RST hi) ;* Input - Word to be sent is in RegHi:RegLo ;* Output - none ;* This routine calls SendData twice with the real data and adds the dummy writes ;*************************************************************************** WriteReg BCF PORTA,STROBE ; set STROBE lo BCF PORTA,DRDY ; set DRDY lo MOVF RegHi,0 ; move RegHi to W MOVWF Temp ; move W to Temp CALL SendData ; bit-bang 8 bits (most-significant) MOVF RegLo,0 ; move RegLo to W MOVWF Temp ; move W to Temp CALL SendData ; bit-band 8 bits (least-significant) BSF PORTA,DRDY ; signal end of transaction MOVLW #0x04 ; NOW send four dummy clocks to latch data MOVWF Count ; initialize Count to 4 BCF PORTA,DATAIN ; set DATAIN lo LOOP4 BSF PORTA,STROBE ; toggle STROBE (4 extra STROBE pulses) BCF PORTA,STROBE DECFSZ Count ; decrement counter GOTO LOOP4 ; loop 4 times RETURN ; return from subroutine ;*************************************************************************** ;* ;* Routine - SendData (keeps /DRDY lo and /RST hi) ;* Input - Byte to be transmitted is passed in Temp ;* Output - none ;* This routine sends 1 byte to the CS6420 MCR ;*************************************************************************** SendData MOVLW #0x08 MOVWF Count ; initialize Count to 8 LOOP8 RLF Temp,1 ; rotate byte left one BTFSC STATUS,CARRY ; if carry bit = 1, BSF PORTA,DATAIN ; set DATAIN hi BTFSS STATUS,CARRY ; if carry bit = 0, BCF PORTA,DATAIN ; set DATAIN lo BSF PORTA,STROBE ; clock data in BCF PORTA,STROBE DECFSZ Count,1 ; decrement counter GOTO LOOP8 ; loop 8 times BCF PORTA,DATAIN ; set DATAIN high RETURN ;*************************************************************************** ;* ;* Routine - Delay ;* Input - none ;* Output - none ;* This routine is a software delay ;*************************************************************************** Delay CLRF DelayTime ; implement when needed DelayLoop MOVLW 0x34 ; Count 100 or 0x34 MOVWF DelayMore Delay2 DECFSZ DelayMore,1 ; loop 100 times GOTO Delay2 DECFSZ DelayTime,1 ; loop 255 times GOTO DelayLoop RETURN end 12 AN106Rev1 * Notes * |
Price & Availability of AN106
 |
|
|
|
|
All Rights Reserved © IC-ON-LINE 2003 - 2022 |
| [Add Bookmark] [Contact Us] [Link exchange] [Privacy policy] |
|
Mirror Sites : [www.datasheet.hk]
[www.maxim4u.com] [www.ic-on-line.cn]
[www.ic-on-line.com] [www.ic-on-line.net]
[www.alldatasheet.com.cn]
[www.gdcy.com]
[www.gdcy.net] |