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 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