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标题: PIC单片机的I2C读写源程序 [打印本页]

作者: winnie 时间: 2009-5-5 17:36
标题: PIC单片机的I2C读写源程序
;*****************************************************************************
;**  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 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
;
ERR1 EQU    0             ; Error flag
;
; Instruction Destination Bits
;
F    EQU    1
W    EQU    0
;
; 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(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.
;
ERR
BTFSS FLAG,ERR1    ; Remain as first error encountered
MOVWF ERCODE       ; Save error code
BSF    FLAG,ERR1    ; 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,ERR1    ; Remain as first error encountered
MOVWF ERCODE       ; Save error code
BSF    FLAG,ERR1    ; 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,ERR1    ; Remain as first error encountered
MOVWF ERCODE       ; Save error code
BSF    FLAG,ERR1    ; 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,ERR1    ; Yes.
MOVWF ERCODE       ; Save error code
BSF    FLAG,ERR1    ; 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, F       ; 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, F       ; 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, F       ; Rotate TXBUF left
SKPC                   ; f(6) ---> f(7)
BCF    TXBUF,0       ; f(7) ---> carry
SKPNC                ; carry ---> f(0)
BSF    TXBUF,0
DECFSZ  COUNT, F       ; 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, F          ;reduce count
goto dly1          ;loop
retlw 0
;
org    0x1FF
goto start
;
END

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