; ********** READ KEYBOARD ROUTINE **********
; 
; 	ENTRY:	NO PARAMETERS.
;	EXIT:	(A) = KEY CONVERTED TO KBLUT VALUE OR 0
;                 IF NO KEY HAS BEEN PRESSED.
; **************************************************

.ORG	0000h

		LD	SP,	0080h	; ADDED FOR TESTING PURPOSES.
		CALL	READKB	; ADDED FOR TESTING PURPOSES.
		HALT			; ADDED FOR TESTING PURPOSES.
		
; SCAN 7 ROWS.
READKB:	LD	HL,	3801h	; ROW 0 ADDRESS. H=38 L=01.
REA010:	LD	A,	(HL)	; GET ROW VALUE.
		OR	A			; TEST FOR ZERO.
		JP	NZ,	REA020	; GO IF KEY THERE.
		SLA	L			; SHIFT ROW ADDRESS. L=02 THEN 04 THEN 08, ETC.
		RET	M			; GO IF LAST ROW & NO PRESS. M = S(IGN) FLAG IS SET.
		JP	REA010		; MORE ROWS TO GO.

;CONVERT ROW, COLUMN TO INDEX	
REA020:	LD	C,	A		; ROW VALUE.
		XOR	A			; ZERO A REGISTER.
REA025:	SRL	L			; SHIFT ADDRESS.
		JP	C,	REA035	; GO IF DONE.
REA030:	ADD	A,	8		; ROW * 8.
		JP	REA025		; CONTINUE.
REA035: LD	B,	0FFh	; COLUMN COUNT.
REA040:	INC	B			; BUMP COUNT.
		SRL	C			; SHIFT ROW VALUE.
		JP	NC,	REA040	; CONTINUE UNTIL "1" OUT.
		ADD	A,	B		; NOW ROW * 8 + COLUMN IN A.
		LD	C,	A		; TRANSFER TO C.

; FIND TABLE ENTRY
		LD	A,	(3880h)	; SHIFT ROW ADDRESS.
		OR	A			; TEST FOR SHIFT KEY.
		JP	Z,	REA045	; GO IF NONE.
		LD	A,	56
REA045:	ADD	A,	C		; ADD HASH + SHIOFT * 56.
		LD	C,	A		; NOW ROW * 8 + COLUMN * SHIFT * 56.
		LD	B,	0		; NOW IN BC.
		LD	HL,	KBLUT	; ADDRESS OF KEYBOARD LOOK UP TABLE.
		ADD HL,	BC		; POINT TO CODE.
		LD	A,	(HL)	; GET VALUE.

; DEBOUNCE DELAY
		LD	HL,	8448	; 100MS DELAY.
		LD	BC, -1		; DECREMENT.
REA050:	ADD	HL,	BC		; DECREMENT COUNT.
		JP	C,	REA050	; GO IF NOT DONE.
		RET				; RETURN WITH CODE IN A REGISTER.
		
; KEYBOARD LOOK UP TABLE
KBLUT:	.DW	8		; ROW 0 LC.
		.DW	8		; ROW 1 LC.
		.DW	8		; ROW 2 LC.
		.DW	8		; ROW 3 LC.
		.DW	8		; ROW 4 LC.
		.DW	8		; ROW 5 LC.
		.DW	8		; ROW 6 LC.
		.DW	8		; ROW 0 LC.
		.DW	8		; ROW 1 LC.
		.DW	8		; ROW 2 LC.
		.DW	8		; ROW 3 LC.
		.DW	8		; ROW 4 LC.
		.DW	8		; ROW 5 LC.
		.DW	8		; ROW 6 LC.

.END