Listing 1--I2C EEPROM-uC-Interface Routine

DEVADDR	equ	0a0h	; EPROM I2C device address

scl	bit	p3.4
sda	bit	p3.5

; register usage
; r0	buf_ptr           ; pointer to internal RAM buffer for block transfers
; r1	count             ; byte count for block transfers
; r2	addr_lo           ; 2-byte memory address (up to 11 bits used)
; r3	addr_hi
; r4	scratch           ; used internally

write_block:            ; write block from RAM to EEPROM
	acall	send_full_address
	jc	fin
wblop:
	mov	a, @r0
	inc	r0
	acall	shift_out
	jc	stop
	djnz	r1, wblop
	sjmp	stop

write_byte:             ; write single byte from ACC to EEPROM
	push	acc
	acall	send_full_address
	pop	acc
	jc	fin
	acall	shift_out
	sjmp	stop

read_block:             ; read block from EEPROM to RAM
                        ; 342 + 102 * nbytes
	acall	send_full_address
	jc	fin
	acall	send_devaddr_rd
	jnc	rb1
	ret

rblop:
	mov	a, #0ffh    ; input data from SDA and send ACK
	acall	shift
	setb	SDA
	mov	@r0, a
	inc	r0
rb1:	djnz	r1, rblop   ; 2 + 102 * nbytes
	acall	shift_in_nak
	mov	@r0, a
	inc	r0
	sjmp	end_read

read_random:            ; read random byte from EEPROM to ACC
                        ; 448 C
	acall	send_full_address
	jc	fin

read_current:           ; read next byte from active EEPROM page to ACC
                        ; 224 C
	acall	send_devaddr_rd
	jc	fin
	acall	shift_in_nak
end_read:               ; 10 C
	clr	c
stop:                   ; Send STOP
                        ; 9 C
	clr	SDA
	setb	SCL
	nop
	nop
	nop
	nop
	setb	SDA         ; 4.7us after SCL
                        ; SCL & SDA high.
	ret

send_full_address:      ; 220 C
	clr	c
	acall	send_devaddr  ; send device address
	jc	fin
                        ; send byte address
	mov	a, r2
	sjmp	soasc

send_devaddr_rd:        ; 112 C
	setb	c
send_devaddr:           ; 111 C
                        ; Send START
	setb	SCL
				
	jnb	SCL, bbsy   ; Check if bus available
	jnb	SDA, bbsy
	clr	SDA         ; min. 4.7 us after SCL high
	mov	a, r3
	rlc	a
	orl	a, #DEVADDR
	clr	SCL         ; min. 4.0 us after SDA low
                        ; SCL & SDA low.
	; send device id, 3 msbits of address and rw bit (from c)
soasc:                  ; 101 C
	acall	shift_out
	jc	stop
fin:
	ret

bbsy:                   ; bus not available
	setb	c
	ret

; Shift out/in a byte from/to A, msb first and ACK bit from/to C.
; SCL low, SDA high on entry and exit.

shift_in_nak:           ; 96 C
	mov	a, #0ffh    ; all ones - input data from SDA
shift_out:              ; 95 C
	setb	c           ; 9th bit - output NAK/release SDA for ACK
shift:                  ; 94 C
	mov	r4, #9      ; 8 bits + ack
shlop:
      ; 3.5 us CLK low to data valid
	rlc	a           ; move bit into C
	mov	SDA, c
	setb	SCL
	nop
	nop
	mov	c, SDA
	clr	SCL         ; min. 4 us
	djnz	r4, shlop
	ret               ; ACK in C

	end