PIC的I2C读写程序

*****************************************           PIC的I2C读写程序           *****************************************TITLE " TWO WIRE/I2C BUS INTERFACE WITH PIC16C5x ";LIST P=16C54;;*****************************************************************************;**  Two wire/I2C Bus READ/WRITE Sample Routines of Microchip's;**  24Cxx / 85Cxx serial CMOS EEPROM interfacing to a ;**  PIC16C54 8-bit CMOS single chip microcomputer;**  Revsied Version 2.0 (4/2/92).;**;**     Part use = PIC16C54-XT/JW                                           ;**  Note:  1) All timings are based on a reference crystal frequency of 2MHz;**            which is equivalent to an instruction cycle time of 2 usec.;**         2) Address and literal values are read in octal unless otherwise;**            specified.;;;       Program:          I2CBUS.ASM ;       Revision Date:   ;                         12-12-95      Compatibility with MPASMWIN 1.30;;********************************************************************** ;;*****************************************************************************;;-----------------------------------------------------------------------------;       Files Assignment;-----------------------------------------------------------------------------;PC      EQU     2               ; Program counterSTAT    EQU     3               ; PIC status byteFSR     EQU     4               ; File Select RegisterRA      EQU     5               ; Port A use to select device addressRB      EQU     6               ; RB7 = SDA, RB6 = SCL;STATUS  EQU     08              ; Status registerFLAG    EQU     09              ; Common flag bits registerEEPROM  EQU     0A              ; Bit bufferERCODE  EQU     0B              ; Error code (to indicate bus status)ADDR    EQU     10              ; Address registerDATAI   EQU     11              ; Stored data input registerDATAO   EQU     12              ; Stored data output registerSLAVE   EQU     13              ; Device address (1010xxx0)TXBUF   EQU     14              ; TX bufferRXBUF   EQU     15              ; RX bufferCOUNT   EQU     16              ; Bit counter;TIMER0  EQU     18              ; Delay timer0TIMER1  EQU     19              ; Delay timer1;;;-----------------------------------------------------------------------------;                     Bit Assignments;-----------------------------------------------------------------------------;; Status bits;Z       EQU     2C       EQU     0;; FLAG Bits;ERR1    EQU     0               ; Error flag;; Instruction Destination Bits;F       EQU     1W       EQU     0;; EEPROM Bits;DI      EQU     7               ; EEPROM inputDO      EQU     6               ; EEPROM output;; I2C Device Bits;SDA     EQU     7               ; RB7, data in/outSCL     EQU     6               ; RB6, serial clock;;END FILES/BITS EQUATEPAGE;;-----------------------------------------------------------------------------;       Two wire/I2C - CPU communication error status table and subroutine;-----------------------------------------------------------------------------;  input  :     W-reg   = error code;  output :     ERCODE  = error code;           FLAG(ERR1) = 1;;         code          error status mode;       -------         ------------------------------------------------------;           1   :       SCL locked low by device (bus is still busy);           2   :       SDA locked low by device (bus is still busy);           3   :       No acknowledge from device (no handshake);           4   :       SDA bus not released for master to generate STOP bit;-----------------------------------------------------------------------------;;Subroutine to identify the status of the serial clock (SCL) and serial data;(SDA) condition according to the error status table. Codes generated are;useful for bus/device diagnosis.;ERRBTFSS   FLAG,ERR1       ; Remain as first error encounteredMOVWF   ERCODE          ; Save error codeBSF     FLAG,ERR1       ; Set error flagRETLW   0;;-----------------------------------------------------------------------------;       START bus communication routine;-----------------------------------------------------------------------------;       input   : none;       output  : initialize bus communication;-----------------------------------------------------------------------------;;Generate START bit (SCL is high while SDA goes from high to low transition);and check status of the serial clock.BSTARTMOVLW   B'00111111'     ; Put SCL, SDA line in output stateTRIS    RB;***************************************************************************bsf     RB,SDA          ;make sure sda is high;***************************************************************************BSF     RB,SCL          ; Set clock highMOVLW   1               ; Ready error status code 1BTFSS   RB,SCL          ; Locked?CALL    ERR             ; SCL locked low by deviceBCF     RB,SDA          ; SDA goes low during SCL highNOP                     ; Timing adjustmentNOPNOPBCF     RB,SCL          ; Start clock trainRETLW   0;;END SUBPAGE;;-----------------------------------------------------------------------------;       STOP bus communication routine;-----------------------------------------------------------------------------;       Input   :       None;       Output  :       Bus communication, STOP condition;-----------------------------------------------------------------------------;;Generate STOP bit (SDA goes from low to high during SCL high state);and check bus conditions.;BSTOP;****************************************************************************MOVLW   B'00111111'     ; Put SCL, SDA line in output stateTRIS    RB;****************************************************************************BCF     RB,SDA          ; Return SDA to lowBSF     RB,SCL          ; Set SCL highnopnopnopMOVLW   1               ; Ready error code 1BTFSS   RB,SCL          ; High?CALL    ERR             ; No, SCL locked low by deviceBSF     RB,SDA          ; SDA goes from low to high during SCL highMOVLW   4               ; Ready error code 4BTFSS   RB,SDA          ; High?CALL    ERR             ; No, SDA bus not release for STOPRETLW   0;;END SUB;;-----------------------------------------------------------------------------;       Serial data send from PIC to serial EEPROM, bit-by-bit subroutine;-----------------------------------------------------------------------------;       Input   :       None;       Output  :       To (DI) of serial EEPROM device;-----------------------------------------------------------------------------;BITINMOVLW   B'10111111'     ; Force SDA line as inputTRIS    RBBSF     RB,SDA          ; Set SDA for inputBCF     EEPROM,DIBSF     RB,SCL          ; Clock highMOVLW   1BTFSC   RB,SCL          ; Skip if SCL  is highGOTO    BIT1BTFSS   FLAG,ERR1       ; Remain as first error encounteredMOVWF   ERCODE          ; Save error codeBSF     FLAG,ERR1       ; Set error flagBIT1BTFSC   RB,SDA          ; Read SDA pinBSF     EEPROM,DI       ; DI = 1NOP                     ; DelayBCF     RB,SCL          ; Return SCL to low     RETLW   0;;END SUBPAGE;;-----------------------------------------------------------------------------;       Serial data receive from serial EEPROM to PIC, bit-by-bit subroutine;-----------------------------------------------------------------------------;       Input   :       EEPROM file;       Output  :       From (DO) of serial EEPROM device to PIC;-----------------------------------------------------------------------------;BITOUTMOVLW   B'00111111'     ; Set SDA, SCL as outputsTRIS    RBBTFSS   EEPROM,DOGOTO    BIT0BSF     RB,SDA          ; Output bit 0MOVLW   2BTFSC   RB,SDA          ; Check for error code 2GOTO    CLK1BTFSS   FLAG,ERR1       ; Remain as first error encounteredMOVWF   ERCODE          ; Save error codeBSF     FLAG,ERR1       ; Set error flagGOTO    CLK1            ; SDA locked low by device;BIT0BCF     RB,SDA          ; Output bit 0NOP                     ; DelayNOPNOPCLK1BSF     RB,SCLMOVLW   1               ; Error code 1BTFSC   RB,SCL          ; SCL locked low?GOTO    BIT2            ; No.BTFSS   FLAG,ERR1       ; Yes.MOVWF   ERCODE          ; Save error codeBSF     FLAG,ERR1       ; Set error flagBIT2NOPNOPBCF     RB,SCL          ; Return SCL to lowRETLW   0;;END SUBPAGE;;;-----------------------------------------------------------------------------;       RECEIVE         DATA    subroutine;-----------------------------------------------------------------------------;       Input   :       None;       Output  :       RXBUF = Receive 8-bit data;-----------------------------------------------------------------------------;RXMOVLW   .8              ; 8 bits of dataMOVWF   COUNTCLRF    RXBUF;RXLPRLF     RXBUF, F        ; Shift data to bufferSKPCBCF     RXBUF,0         ; carry ---> f(0)SKPNCBSF     RXBUF,0CALL    BITINBTFSC   EEPROM,DIBSF     RXBUF,0         ; Input bit =1DECFSZ  COUNT, F        ; 8 bits?GOTO    RXLPBSF     EEPROM,DO       ; Set acknowledge bit = 1CALL    BITOUT          ; to STOP further inputRETLW   0;;END SUB;;-----------------------------------------------------------------------------;       TRANSMIT        DATA    subroutine;-----------------------------------------------------------------------------;       Input   :       TXBUF;       Output  :       Data X'mitted to EEPROM device;-----------------------------------------------------------------------------;TXMOVLW   .8MOVWF   COUNT;TXLPBCF     EEPROM,DO       ; Shift data bit out.BTFSC   TXBUF,7         ; If shifted bit = 0, data bit = 0BSF     EEPROM,DO       ; Otherwise data bit = 1CALL    BITOUT          ; Serial data outRLF     TXBUF, F        ; Rotate TXBUF leftSKPC                    ; f(6) ---> f(7)BCF     TXBUF,0         ; f(7) ---> carrySKPNC                   ; carry ---> f(0)BSF     TXBUF,0DECFSZ  COUNT, F        ; 8 bits done?GOTO    TXLP            ; No.CALL    BITIN           ; Read acknowledge bitMOVLW   3BTFSC   EEPROM,DI       ; Check for acknowledgementCALL    ERR             ; No acknowledge from deviceRETLW   0;;END SUBPAGE;;-----------------------------------------------------------------------------;       BYTE-WRITE, write one byte to EEPROM device;-----------------------------------------------------------------------------;       Input   :       DATAO= data to be written;                       ADDR    = destination address;                       SLAVE   = device address (1010xxx0);       Output  :       Data written to EEPROM device;-----------------------------------------------------------------------------;ORG     080             ; The location for BYTE-WRITE routine can be;                               ; assigned anywhere between (377-777) octal.WRBYTEMOVF    SLAVE,W         ; Get SLAVE addressMOVWF   TXBUF           ; to TX bufferCALL    BSTART          ; Generate START bitCALL    TX              ; Output SLAVE addressMOVF    ADDR,W          ; Get WORD addressMOVWF   TXBUF           ; into bufferCALL    TX              ; Output WORD addressMOVF    DATAO,W         ; Move DATA MOVWF   TXBUF           ; into bufferCALL    TX              ; Output DATA and detect acknowledgementCALL    BSTOP           ; Generate STOP bitgoto    wrt_end;;;;-----------------------------------------------------------------------------;       BYTE-READ, read one byte from serial EEPROM device;-----------------------------------------------------------------------------;       Input   :       ADDR    = source address;                       SLAVE   = device address (1010xxx0);       Output  :       DATAI   = data read from serial EEPROM;-----------------------------------------------------------------------------;ORG     0C0             ; The location for BYTE-READ routine can be;                               ; assigned anywhere between (377-777) octal.RDBYTEMOVF    SLAVE,W         ; Move SLAVE address MOVWF   TXBUF           ; into buffer (R/W = 0)CALL    BSTART          ; Generate START bitCALL    TX              ; Output SLAVE address. Check ACK.MOVF    ADDR,W          ; Get WORD addressMOVWF   TXBUFCALL    TX              ; Output WORD address. Check ACK.CALL    BSTART          ; START READ (if only one device isMOVF    SLAVE,W         ; connected to the I2C bus)MOVWF   TXBUFBSF     TXBUF,0         ; Specify READ mode (R/W = 1)CALL    TX              ; Output SLAVE addressCALL    RX              ; READ in data and acknowledgeCALL    BSTOP           ; Generate STOP bitMOVF    RXBUF,W         ; Save data from bufferMOVWF   DATAI           ; to DATAI file.goto    rd_end;;Test program to read and write ramdomstartmovlw   0AE             ;set A2=A1=A0=1movwf   SLAVE           ;       /movlw   2               ;set r/w loc. = 2movwf   ADDR            ;       /movlw   55              ;write 55 to SEEPROMmovwf   DATAO           ;       /goto    WRBYTE          ;write a bytewrt_endcall    delay           ;wait for write;operation (internal)goto    RDBYTE          ;read back datard_endmovlw   55              ;test if readxorwf   DATAI,W         ;correct?btfss   STAT,Z          ;yes then skipwrong   goto    wrongcorrectgoto    correct;;At 2.0Mhz, delay = approx. 3mS.delayclrf    1F              ;clear last locationdly1nopnopnopdecfsz  1F, F           ;reduce countgoto    dly1            ;loopretlw   0;org     0x1FFgoto    start;END