PIC的一个读写I2C程序

PIC的一个读写I2C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.
;********************************************************
;
;-----------------------------------------------------------------------------
;       Files Assignment
;-----------------------------------------------------------------------------
;
PC      EQU     2               ; Program counter
STAT    EQU     3               ; PIC status byte
FSR     EQU     4               ; File Select Register
RA      EQU     5               ; Port A use to select device address
RB      EQU     6               ; RB7 = SDA, RB6 = SCL
;
STATUS  EQU     08              ; Status register
FLAG    EQU     09              ; Common flag bits register
EEPROM  EQU     0A              ; Bit buffer
ERCODE  EQU     0B              ; Error code (to indicate bus status)
ADDR    EQU     10              ; Address register
DATAI   EQU     11              ; Stored data input register
DATAO   EQU     12              ; Stored data output register
SLAVE   EQU     13              ; Device address (1010xxx0)
TXBUF   EQU     14              ; TX buffer
RXBUF   EQU     15              ; RX buffer
COUNT   EQU     16              ; Bit counter
;
TIMER0  EQU     18              ; Delay timer0
TIMER1  EQU     19              ; Delay timer1
;
;
;-----------------------------------------------------------------------------
;                     Bit Assignments
;-----------------------------------------------------------------------------
;
; Status bits
;
Z       EQU     2
C       EQU     0
;
; FLAG Bits
;
ERROR   EQU     0               ; Error flag
;
; EEPROM Bits
;
DI      EQU     7               ; EEPROM input
DO      EQU     6               ; EEPROM output
;
; I2C Device Bits
;
SDA     EQU     7               ; RB7, data in/out
SCL     EQU     6               ; RB6, serial clock
;
;END FILES/BITS EQUATE
 PAGE
;
;-----------------------------------------------------------------------------
;       Two wire/I2C - CPU communication error status table and subroutine
;-----------------------------------------------------------------------------
;  input  :     W-reg   = error code
;  output :     ERCODE  = error code
;           FLAG(ERROR) = 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.
;
ERR
 BTFSS   FLAG,ERROR      ; Remain as first error encountered
 MOVWF   ERCODE          ; Save error code
 BSF     FLAG,ERROR      ; Set error flag
 RETLW   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.
BSTART
 MOVLW   B'00111111'     ; Put SCL, SDA line in output state
 TRIS    RB
;**************************************************************
 bsf     RB,SDA          ;make sure sda is high
;*******************************************************
 BSF     RB,SCL          ; Set clock high
 MOVLW   1               ; Ready error status code 1
 BTFSS   RB,SCL          ; Locked?
 CALL    ERR             ; SCL locked low by device
 BCF     RB,SDA          ; SDA goes low during SCL high
 NOP                     ; Timing adjustment
 NOP
 NOP
 BCF     RB,SCL          ; Start clock train
 RETLW   0
;
;END SUB
 PAGE
;
;-----------------------------------------------------------------------------
;       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 state
 TRIS    RB
;**************************************************************
 BCF     RB,SDA          ; Return SDA to low
 BSF     RB,SCL          ; Set SCL high
 nop
 nop
 nop
 MOVLW   1               ; Ready error code 1
 BTFSS   RB,SCL          ; High?
 CALL    ERR             ; No, SCL locked low by device
 BSF     RB,SDA          ; SDA goes from low to high during SCL high
 MOVLW   4               ; Ready error code 4
 BTFSS   RB,SDA          ; High?
 CALL    ERR             ; No, SDA bus not release for STOP
 RETLW   0
;
;END SUB
;
;-----------------------------------------------------------------------------
;       Serial data send from PIC to serial EEPROM, bit-by-bit subroutine
;-----------------------------------------------------------------------------
;       Input   :       None
;       Output  :       To (DI) of serial EEPROM device
;-----------------------------------------------------------------------------
;
BITIN
 MOVLW   B'10111111'     ; Force SDA line as input
 TRIS    RB
 BSF     RB,SDA          ; Set SDA for input
 BCF     EEPROM,DI
 BSF     RB,SCL          ; Clock high
 MOVLW   1
 BTFSC   RB,SCL          ; Skip if SCL  is high
 GOTO    BIT1
 BTFSS   FLAG,ERROR      ; Remain as first error encountered
 MOVWF   ERCODE          ; Save error code
 BSF     FLAG,ERROR      ; Set error flag
BIT1
 BTFSC   RB,SDA          ; Read SDA pin
 BSF     EEPROM,DI       ; DI = 1
 NOP                     ; Delay
 BCF     RB,SCL          ; Return SCL to low    
 RETLW   0
;
;END SUB
 PAGE
;
;-----------------------------------------------------------------------------
;       Serial data receive from serial EEPROM to PIC, bit-by-bit subroutine
;-----------------------------------------------------------------------------
;       Input   :       EEPROM file
;       Output  :       From (DO) of serial EEPROM device to PIC
;-----------------------------------------------------------------------------
;
BITOUT
 MOVLW   B'00111111'     ; Set SDA, SCL as outputs
 TRIS    RB
 BTFSS   EEPROM,DO
 GOTO    BIT0
 BSF     RB,SDA          ; Output bit 0
 MOVLW   2
 BTFSC   RB,SDA          ; Check for error code 2
 GOTO    CLK1
 BTFSS   FLAG,ERROR      ; Remain as first error encountered
 MOVWF   ERCODE          ; Save error code
 BSF     FLAG,ERROR      ; Set error flag
 GOTO    CLK1            ; SDA locked low by device
;
BIT0
 BCF     RB,SDA          ; Output bit 0
 NOP                     ; Delay
 NOP
 NOP
CLK1
 BSF     RB,SCL
 MOVLW   1               ; Error code 1
 BTFSC   RB,SCL          ; SCL locked low?
 GOTO    BIT2            ; No.
 BTFSS   FLAG,ERROR      ; Yes.
 MOVWF   ERCODE          ; Save error code
 BSF     FLAG,ERROR      ; Set error flag
BIT2
 NOP
 NOP
 BCF     RB,SCL          ; Return SCL to low
 RETLW   0
;
;END SUB
 PAGE
;
;
;-----------------------------------------------------------------------------
;       RECEIVE         DATA    subroutine
;-----------------------------------------------------------------------------
;       Input   :       None
;       Output  :       RXBUF = Receive 8-bit data
;-----------------------------------------------------------------------------
;
RX
 MOVLW   .8              ; 8 bits of data
 MOVWF   COUNT
 CLRF    RXBUF
;
RXLP
 RLF     RXBUF           ; Shift data to buffer
 SKPC
 BCF     RXBUF,0         ; carry ---> f(0)
 SKPNC
 BSF     RXBUF,0
 CALL    BITIN
 BTFSC   EEPROM,DI
 BSF     RXBUF,0         ; Input bit =1
 DECFSZ  COUNT           ; 8 bits?
 GOTO    RXLP
 BSF     EEPROM,DO       ; Set acknowledge bit = 1
 CALL    BITOUT          ; to STOP further input
 RETLW   0
;
;END SUB
;
;-----------------------------------------------------------------------------
;       TRANSMIT        DATA    subroutine
;-----------------------------------------------------------------------------
;       Input   :       TXBUF
;       Output  :       Data X'mitted to EEPROM device
;-----------------------------------------------------------------------------
;
TX
 MOVLW   .8
 MOVWF   COUNT
;
TXLP
 BCF     EEPROM,DO       ; Shift data bit out.
 BTFSC   TXBUF,7         ; If shifted bit = 0, data bit = 0
 BSF     EEPROM,DO       ; Otherwise data bit = 1
 CALL    BITOUT          ; Serial data out
 RLF     TXBUF           ; Rotate TXBUF left
 SKPC                    ; f(6) ---> f(7)
 BCF     TXBUF,0         ; f(7) ---> carry
 SKPNC                   ; carry ---> f(0)
 BSF     TXBUF,0
 DECFSZ  COUNT           ; 8 bits done?
 GOTO    TXLP            ; No.
 CALL    BITIN           ; Read acknowledge bit
 MOVLW   3
 BTFSC   EEPROM,DI       ; Check for acknowledgement
 CALL    ERR             ; No acknowledge from device
 RETLW   0
;
;END SUB
 PAGE
;
;-----------------------------------------------------------------------------
;       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.
WRBYTE
 MOVF    SLAVE,W         ; Get SLAVE address
 MOVWF   TXBUF           ; to TX buffer
 CALL    BSTART          ; Generate START bit
 CALL    TX              ; Output SLAVE address
 MOVF    ADDR,W          ; Get WORD address
 MOVWF   TXBUF           ; into buffer
 CALL    TX              ; Output WORD address
 MOVF    DATAO,W         ; Move DATA
 MOVWF   TXBUF           ; into buffer
 CALL    TX              ; Output DATA and detect acknowledgement
 CALL    BSTOP           ; Generate STOP bit
 goto    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.
RDBYTE
 MOVF    SLAVE,W         ; Move SLAVE address
 MOVWF   TXBUF           ; into buffer (R/W = 0)
 CALL    BSTART          ; Generate START bit
 CALL    TX              ; Output SLAVE address. Check ACK.
 MOVF    ADDR,W          ; Get WORD address
 MOVWF   TXBUF
 CALL    TX              ; Output WORD address. Check ACK.
 CALL    BSTART          ; START READ (if only one device is
 MOVF    SLAVE,W         ; connected to the I2C bus)
 MOVWF   TXBUF
 BSF     TXBUF,0         ; Specify READ mode (R/W = 1)
 CALL    TX              ; Output SLAVE address
 CALL    RX              ; READ in data and acknowledge
 CALL    BSTOP           ; Generate STOP bit
 MOVF    RXBUF,W         ; Save data from buffer
 MOVWF   DATAI           ; to DATAI file.
 goto    rd_end
;
;Test program to read and write ramdom
start
 movlw   0AE             ;set A2=A1=A0=1
 movwf   SLAVE           ;       /
 movlw   2               ;set r/w loc. = 2
 movwf   ADDR            ;       /
 movlw   55              ;write 55 to SEEPROM
 movwf   DATAO           ;       /
 goto    WRBYTE          ;write a byte
wrt_end
 call    delay           ;wait for write
    ;operation (internal)
 goto    RDBYTE          ;read back data
rd_end
 movlw   55              ;test if read
 xorwf   DATAI,W         ;correct?
 btfss   STAT,Z          ;yes then skip
wrong  
 goto    wrong
correct
 goto    correct
;
;At 2.0Mhz, delay = approx. 3mS.
delay
 clrf    1F              ;clear last location
dly1
 nop
 nop
 nop
 decfsz  1F              ;reduce count
 goto    dly1            ;loop
 retlw   0
;
 org     0x1FF
 goto    start
;
 END