\prog;XI2C8574.asm|I/O expander test
;JDN 280301 
.Proc	16F84
RB0	= 5	; bit on Status register that control Bank1
.Macro	Bank0to1
	Set	Status:#RB0
.Endmacro
.Macro	Bank1to0
	Clr	Status:#RB0
.Endmacro

\b;PortA
bSCK	= 0
bSDA	= 1
DirA	= 2'00011	; Bits 0 and 1 as inputs
PortI2C	= 5
TrisI2C	= PortI2C

Ad8574	= 16'40

\b;Variables
.Loc	16'0C	; begin of variables
.Ins	Xi2cV.asi

.Ins	Xi2cM.asi	; macros

\b;Programme
.Loc	0	; program start
Deb:	Move	#DirA,W
	Move	W,TrisA
	Clr	PortA	; important for SCK SDA

	Move	#Ad8574,W
	Move	W,AdSlave

	Move	#Ad8574,W	; Declared as 16'40 to 16'4E, according to address inputs
	Move	W,AdSlave
	Move	#2'00001111,W
	Move	W,Datai2c   	; Data direction initialized
	Call	WrSingleI2C
Loop:
	Call	RdSingleI2C	; Result in W and AdI2C
	Swap	AdI2C,W
	Or	#2'00001111,W
	Move	W,DataI2C
	Call	WrSingleI2C
	Call	Wait	; space on the scope
			; to ease synchronization
	Jump	Loop

WrSingleI2C:
	Move	AdSlave,W
	Move	W,ADi2c
	Start
	Call	WriteI2C
	Move	DataI2C,W
	Move	W,ADi2c
	Call	WriteI2C
	Stop
	Ret

RdSingleI2C:
	Move	AdSlave,W
	Or	#00000001,W
	Move	W,ADi2c
	Start
	Call	WriteI2C
	Call	ReadI2C
	Call	GiveNAckR
	Stop
	Ret

.Ins	Xi2cR.asi

\rout:Wait|1ms wait
Wait:	Clr	W
 W$:	Add	#-1,W	; 4 us loop
	Skip,EQ  	; repeated 256 times
	Jump	W$
	Ret
.End