dt-107-005cn.txt

8051单片机使用ASM对IIC器件访问的底层函数

;*******************************************************************************
OutByte:
	setb    C
OutByteLoop:
	rlc     A                       ; SHIFT OUT THE BYTE, MSB FIRST
	jnc     OutByte0
	setb    P1.SDAbit
	ajmp    OutByte1
OutByte0:
	clr     P1.SDAbit
OutByte1:
	acall   ClockPulse              ; CLOCK THE DATA INTO THE IIC Device
	cjne    A,#10000000b,OutByteNxt ; SKIP IF NOT DONE
	jmp     GetACK                  ; CHECK FOR AN ACK FROM THE DEVICE
OutByteNxt:
	clr     C                       ; LOOP IF ALL THE BITS HAVE
	ajmp    OutByteLoop             ; NOT BEEN SHIFTED OUT

;******************************************************************************
;** Name: InByte
;** Description: Shifts in a byte from the IIC Device
;** Function: This subroutine shifts in a byte, MSB first, through the
;**             assigned SDA/SCL lines on port 1. After the byte is received
;**             an ACK bit is sent to the IIC Device.
;** Calls:              ClockPulse
;** Input:              None
;** Return Value:       A = Received byte
;** Register Usage:     A
;******************************************************************************
InByte:
	mov     A,#00000001b
	setb    P1.SDAbit               ; SDA LINE FORCED HIGH
InByteNxt:
	acall   ClockPulse              ; CLOCK THE Serial MEMORY AND SHIFT
	rlc     A                       ; INTO ACC. THE LOGIC LEVEL ON THE SDA
	jnc     InByteNxt               ; LINE. THE DEVICE OUTPUTS DATA ON SDA
	ret                             ; MSB FIRST

;******************************************************************************
;** Name: ClockPulse
;** Description: Generate a clock pulse
;** Function: This subroutine forces a high-low transition on the assigned SCL
;**             pin of port 1. It also samples and returns the SDA line state 
;**             during high clock period.
;** Calls:              None
;** Input:              None
;** Return Value:       C = SDA line status
;** Register Usage:     None
;******************************************************************************
ClockPulse:
      nop
	setb    P1.SCLbit               ; BASED ON A 12MHz SYSTEM CRYSTAL THE
	nop                             ; BUS CYCLE TIME IS 1 MICROSEC.
	nop
      nop
	clr     C                       ;
	jnb     P1.SDAbit,ClockPulseLo  ;
	setb    C
ClockPulseLo:
	clr     P1.SCLbit               ; LOWER THE CLOCK LINE
	ret

;******************************************************************************
;** Name: OutACK
;** Description: Send out an ACK bit to the IIC Device
;** Function: This subroutine clocks an ACK bit to the IIC Device.
;**             The ACK cycle acknowledges a properly received data by lowering
;**             the SDA line during this period (9th clock cycle of a received
;**             byte).
;**                 !!!!!!!!!!  RETURN FROM CALL PARENT ROUTINE    !!!!!!!!!!!
;** Calls:              ClockPulse
;** Input:              None
;** Return Value:       None
;** Register Usage:     None
;******************************************************************************
OutACK:
	clr     P1.SDAbit               ; MAKE SURE THAT THE DATA LINE IS LOW   ...
	jmp     ClockPulse              ; CLOCK OUT THE ACK CYCLE

;******************************************************************************
;** Name: GetACK
;** Description: Clock the IIC Device for ACK cycle
;** Function: This subroutine returns the sampled logic level on the SDA during
;**             high clock cycle. The IIC Device holds the SDA line HIGH if
;**             it does not receive the correct number of clocks or it's stuck in
;**             a previously initiated write command.
;** Calls:              ClockPulse
;** Input:              None
;** Return Value:       C = ACKnowledge bit
;** Register Usage:     None
;******************************************************************************
GetACK:
	setb    P1.SDAbit               ; FORCE SDA LINE HIGH
	acall   ClockPulse              ; GENERATE ONE CLOCK PULSE
	ret

;******************************************************************************
;** Name: ACKPoll
;** Description: Wait for an ACK from the IIC Device
;** Function: This subroutine monitors the IIC Device response
;**             following a dummy write command. The program returns when it
;**             either receives an ACK bit or the maximum number of tries is
;**             reached.
;** Calls:              Start, SlavAddr, Stop
;** Input:              None
;** Return Value:       C = ACKnowledge bit [=0 ACK ,=1 No ACK was received]
;** Register Usage:     A, R1
;******************************************************************************
ACKPoll:
	mov     R1,#MaxDelay            ; LOAD MAX NO. OF ACK POLLING CYCLE
ACKPollnxt:
	acall   Start                   ; START THE ACK POLL CYCLE AND
	clr     C                       ; [C=0] WRITE OPERATION BIT
	acall   SlavAddr                ; SEND THE SLAVE ADDRESS. THEN
                                      ; MONITOR THE SDA LINE FOR AN ACK FROM
                                      ; THE IIC Device. TERMINATE THE
	acall   Stop                    ; OPERATION BY A STOP CONDITION.
	jnc     ACKPollExit             ; EXIT IF THE ACK WAS RECEIVED
      djnz    R1,ACKPollnxt           ; LOOP WHILE THE MAXIMUM NO. OF CYCLES
                                      ; HAVE NOT EXPIRED. ELSE RETURN WITH C=1
ACKPollExit:
	ret

;******************************************************************************
;** Name: Start
;** Description: Send a start command to the IIC Device
;** Function: This subroutine generates a start condition on the bus. The start
;**             condition is defined as a high-low transition on the SDA
;**             line while the SCL is high. The start is used at the beginning
;**             of all transactions.
;** Calls:              None
;** Input:              None
;** Return Value:       None
;** Register Usage:     None
;******************************************************************************
Start:
	setb    P1.SDAbit               ; FORCE THE SDA LINE HIGH
	setb    P1.SCLbit               ; FORCE THE SCL CLOCK LINE HIGH
      nop
      nop
      nop
	clr     P1.SDAbit               ; BEFORE TAKING THE SDA LOW
	nop
	nop
	nop
	nop
	clr     P1.SCLbit               ; FORCE THE SCL LOW
	ret

;******************************************************************************
;** Name: Stop
;** Description: Send stop command to the IIC Device
;** Function: This subroutine generates a stop condition on the bus. The stop
;**             condition is defined as a low-high transition on the SDA
;**             line while the SCL is high. The stop is used to indicate end
;**             of current transaction.
;** Calls:              None
;** Input:              None
;** Return Value:       None
;** Register Usage:     None
;******************************************************************************
Stop:
	clr     P1.SDAbit               ; FORCE THE SDA LOW BEFORE TAKING
	setb    P1.SCLbit               ; THE SCL CLOCK LINE HIGH
	nop
	nop
	nop
	nop
	setb    P1.SDAbit               ; FORCE THE SDA HIGH (IDLE STATE)
	ret

;******************************************************************************
;** Name: ResetIIC
;** Description: Resets the IIC Device
;** Function: This subroutine is written for the worst case. System interruptions
;**             caused by brownout or soft error conditions that reset the main
;**             CPU may have no effect on the internal Vcc sensor and reset 
;**             circuit of the IIC Device. These are unpredictable and 
;**             random events that may leave the IIC Device interface
;**             logic in an unknown state. Issuing a Stop command may not be
;**             sufficient to reset the IIC Device.
;** Calls:              Start, Stop
;** Input:              None
;** Return Value:       None
;** Register Usage:     R0
;******************************************************************************
ResetIIC:
	mov     R0,#0AH                 ; APPLY 10 CLOCKS TO THE DEVICE. EACH
ResetNxt:
	acall   Start                   ; CYCLE CONSISTS OF A START/STOP
	acall   Stop                    ; THIS WILL TERMINATE PENDING WRITE
	djnz    R0,ResetNxt             ; COMMAND AND PROVIDES ENOUGH CLOCKS
	ret                             ; FOR REMAINING BITS OF A READ OPERATION

;******************************************************************************
;** END OF IIC Device INTERFACE SOURCE CODE
;******************************************************************************

	END