PIC的一個讀寫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