#include	"c:\miniIDE\hcs12.inc"
		org	$1000
		ds.b	1
		org	$1500
		lds	#$1500
		jsr	openDS1307
		swi
openDS1307	ldaa	#$D0		; place DS1307 ID in A
		jsr	sendSlaveID
		brclr	IBSR,RXAK,sndRegAdr  ; did DS1307 acknowledge?
		ldab	#$FF		; return error code -1
		rts
sndRegAdr	movb	#$07,IBDR	; send out the control register address
		brclr	IBSR,IBIF,*	; wait until the register address is shifted out
		movb	#IBIF,IBSR	; clear the IBIF flag
		brclr	IBSR,RXAK,sndok	; did DS1307 acknowledge?
		ldab	#$FF
		rts
sndok		stab	IBDR		; send out control byte
		brclr	IBSR,IBIF,*	; wait until the control byte is shifted out
		movb	#IBIF,IBSR
		bclr	IBCR,MSSL	; generate stop condition
		rts
sendSlaveID	
		brset	IBSR,IBB,*	; wait until I2C bus is free
		bset	IBCR,TXRX+MSSL	; generate a start condition
		staa	IBDR	; send out the slave address
wait_I2C	brclr	IBSR,IBIF,*	; wait for address transmission to complete
		movb	#IBIF,IBSR	; clear the IBIF flag
		rts	
		end