i2c.asm

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;############################################
;# PROCEDURY pro komunikaci po sbernici	I2C #
;############################################
;
	.global	read_current
	.global	read_random
;
.nolist
.include "param.inc"
.list
;
	.bitcomm I2Cpresent, 1

	.text
	.using	0

read_current:
	; AT24Cxx Current Address Read function.
	; Called with programmable address in A. Returns data in A.
	; Returns CY set to indicate that the bus is not available
	; or that the addressed device failed to acknowledge.
	lcall	start
	jc	x45		; abort if bus not available
	mov	a, #(FADDR | 0b00000001); set fixed address and read operation
	lcall	shout		; send device address
	jc	x44		; abort if no acknowledge
	lcall	shin		; receive data byte
	lcall	NAK		; do not acknowledge byte
	clr	c		; clear error flag
x44:	sjmp	stop
x45:	ret

read_random:
	; AT24Cxx Random Read function.
	; Called with programmable address in A, byte address in
	; register pair DPTR. Returns data in A.
	; Returns CY set to indicate that the bus is not available
	; or that the addressed device failed to acknowledge.
	; Send dummy write command to set internal address.
	lcall	start
	jc	x47		; abort if bus not available
	mov	a, #(FADDR & 0b11111110)	; set fixed address
	lcall	shout		; send device address
	jc	x46		; abort if no acknowledge
	mov	a, DPH		; send high byte of address
	lcall	shout		;
	jc	x46		; abort if no acknowledge
	mov	a, DPL		; send low byte of address
	lcall	shout		;
	jc	x46		; abort if no acknowledge
	; Call Current Address Read function.
	sjmp	read_current
x46:	sjmp	stop
x47:	ret

start:	; Send START, defined as high-to-low SDA with SCL high.
	; Return with SCL, SDA low.
	; Returns CY set if bus is not available.
	setb	SDA
	setb	SCL
	; Verify bus available.
	setb	c		; set error flag
	jnb	SDA, failstart	; jump if not high
	jnb	SCL, failstart	; jump if not high
;	nop			; enforce setup delay and cycle delay
	clr	SDA
;	nop			; enforce hold delay
;	nop			;
;	nop			;
;	nop			;
	nop			;
	clr	SCL
	cpl	c		; clear error flag
failstart:
	ret

stop: 	; Send STOP, defined as low-to-high SDA with SCL high.
	; SCL expected low on entry. Return with SCL, SDA high.
	clr	SDA
	nop			; enforce SCL low and data setup
;	nop
	setb	SCL
;	nop			; enforce setup delay
;	nop			;
;	nop			;
;	nop			;
	nop			;
	setb	SDA
	ret

shout:	; Shift out a byte to the AT24Cxx, most significant bit first.
	; SCL, SDA expected low on entry. Return with SCL low.
	; Called with data to send in A.
	; Returns CY set to indicate failure by slave to acknowledge.
	; Destroys A.
	setb	C		;Ack BIT
shoutLp:rlc	a		; move bit into CY
	mov	SDA, c		; output bit
	nop			; enforce SCL low and data setup
	setb	SCL		; raise clock
	jz	shoutAck
;	nop			; enforce SCL high
;	nop			;
	clr	C		;
	clr	SCL		; drop clock
	sjmp	shoutLp		; next bit
shoutAck:
;	nop			; enforce SCL high
;	nop			;
;	nop			;
;	nop			;
	mov	c, SDA		; get ACK bit
	clr	SCL		; drop ACK clock
	ret

shin:	; Shift in a byte from the AT24Cxx, most significant bit first.
	; SCL expected low on entry. Return with SCL low.
	; Returns received data byte in A.
	mov	a,#1		; stop marker
	setb	SDA		; make SDA an input
shinL:	nop			; enforce SCL low and data setup
;	nop			;
;	nop			;
	setb	SCL		; raise clock
;	nop			; enforce SCL high
	nop			;
	mov	c, SDA		; input bit
	rlc	a		; move bit into byte
	clr	SCL		; drop clock
	jnc	shinL		; next bit
	ret

ACK:	; Clock out an acknowledge bit (low).
	; SCL expected low on entry. Return with SCL, SDA low.
	clr	SDA		; ACK bit
	nop			; enforce SCL low and data setup
;	nop			;
	setb	SCL		; raise clock
;	nop			; enforce SCL high
;	nop			;
	nop			;
	nop			;
	clr	SCL		; drop clock
	ret

NAK:	; Clock out a negative acknowledge bit (high).
	; SCL expected low on entry. Return with SCL low, SDA high.
	setb	SDA		; NAK bit
	nop			; enforce SCL low and data setup
;	nop			;
	setb	SCL		; raise clock
;	nop			; enforce SCL high
;	nop			;
	nop			;
	nop			;
	clr	SCL		; drop clock
	ret

	.section reset_device, #alloc
testI2Cpresent:
	clr	I2Cpresent
	mov	dptr,#0		;offset of ID in I2C EEPROM
	lcall	read_random
	cjne	A,#'@',notI2C
	lcall	read_current
	cjne	A,#'B',notI2C
	lcall	read_current
	cjne	A,#'C',notI2C
	lcall	read_current
	cjne	A,#'L',notI2C
	setb	I2Cpresent
notI2C:
;
;
;&&& end of modul I2C &&&
;
	;; END