;-----------------------------------------------------------------------------
; 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
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本文关键字：程序 PIC单片机，单片机-工控设备 - PIC单片机
