#include "c:\miniide\hcs12.inc"
keyboard	equ	PORTA

get_char	movb	#$F0,DDRA		; configure pins PA7~PA4 for output,PA3~PA0 for input
scan_r0	movb	#$EF,keyboard	; scan the row containing keys 0123
scan_k0	brclr	keyboard,$01,key0	; is key 0 pressed?
scan_k1	brclr	keyboard,$02,key1	; is key 1 pressed?
scan_k2	brclr	keyboard,$04,key2	; is key 2 pressed?
scan_k3	brclr	keyboard,$08,key3	; is key 3 pressed?
		bra	scan_r1
key0		jmp	db_key0
key1		jmp	db_key1
key2		jmp	db_key2
key3		jmp	db_key3
scan_r1	movb	#$DF,keyboard		; scan the row containing keys 4567
scan_k4	brclr	keyboard,$01,key4	; is key 4 pressed?
scan_k5	brclr	keyboard,$02,key5	; is key 5 pressed?
scan_k6	brclr	keyboard,$04,key6	; is key 6 pressed?
scan_k7	brclr	keyboard,$08,key7	; is key 7 pressed?
		bra	scan_r2
key4		jmp	db_key4
key5		jmp	db_key5
key6		jmp	db_key6
key7		jmp	db_key7
scan_r2	movb	#$BF,keyboard		; scan the row containing keys 89AB
		bclr	keyboard,$40		;	"
scan_k8	brclr	keyboard,$01,key8	; is key 8 pressed?
scan_k9	brclr	keyboard,$02,key9	; is key 9 pressed?
scan_kA	brclr	keyboard,$04,keyA	; is key A pressed?
scan_kB	brclr	keyboard,$08,keyB	; is key B pressed?
		bra	scan_r3
key8		jmp	db_key8
key9		jmp	db_key9
keyA		jmp	db_keyA
keyB		jmp	db_keyB
scan_r3	movb	#$7F,keyboard		; scan the row containing keys CDEF
scan_kC	brclr	keyboard,$01,keyC	; is key C pressed?
scan_kD	brclr	keyboard,$02,keyD	; is key D pressed?
scan_kE	brclr	keyboard,$04,keyE	; is key E pressed?
scan_kF	brclr	keyboard,$08,keyF	; is key F pressed?
		jmp	scan_r0
keyC		jmp	db_keyC
keyD		jmp	db_keyD
keyE		jmp	db_keyE
keyF		jmp	db_keyF
; debounce key 0
db_key0	jsr	delay10ms
		brclr	keyboard,$01,getc0
		jmp	scan_k1
getc0		ldaa	#$30		; return the ASCII code of 0
		rts
; debounce key 1
db_key1	jsr	delay10ms
		brclr	keyboard,$02,getc1
		jmp	scan_k2
getc1		ldaa	#$31		; return the ASCII code of 1
		rts
db_key2	jsr	delay10ms
		brclr	keyboard,$04,getc2
		jmp	scan_k3
getc2		ldaa	#$32		; return the ASCII code of 2
		rts
db_key3	jsr	delay10ms
		brclr	keyboard,$08,getc3
		jmp	scan_r1
getc3		ldaa	#$33		; return the ASCII code of 3
		rts
db_key4	jsr	delay10ms
		brclr	keyboard,$01,getc4
		jmp	scan_k5
getc4		ldaa	#$34		; return the ASCII code of 4
		rts
db_key5	jsr	delay10ms
		brclr	keyboard,$02,getc5
		jmp	scan_k6
getc5		ldaa	#$35		; return the ASCII code of 5
		rts
db_key6	jsr	delay10ms
		brclr	keyboard,$04,getc6
		jmp	scan_k7
getc6		ldaa	#$36		; return the ASCII code of 6
		rts
db_key7	jsr	delay10ms
		brclr	keyboard,$08,getc7
		jmp	scan_r2
getc7		ldaa	#$37		; return the ASCII code of 7
		rts
db_key8	jsr	delay10ms
		brclr	keyboard,$01,getc8
		jmp	scan_k9
getc8		ldaa	#$38		; return the ASCII code of 8
		rts
db_key9	jsr	delay10ms
		brclr	keyboard,$02,getc9
		jmp	scan_kA
getc9		ldaa	#$39		; return the ASCII code of 9
		rts
db_keyA	jsr	delay10ms
		brclr	keyboard,$04,getcA
		jmp	scan_kB
getcA		ldaa	#$41		; get the ASCII code of A
		rts
db_keyB	jsr	delay10ms
		brclr	keyboard,$08,getcB
		jmp	scan_r3
getcB		ldaa	#$42		; get the ASCII code of B
		rts
db_keyC	jsr	delay10ms
		brclr	keyboard,$01,getcC
		jmp	scan_kD
getcC		ldaa	#$43		; get the ASCII code of C
		rts
db_keyD	jsr	delay10ms
		brclr	keyboard,$02,getcD
		jmp	scan_kE
getcD		ldaa	#$44		; get the ASCII code of D
		rts
db_keyE	jsr	delay10ms
		brclr	keyboard,$04,getcE
		jmp	scan_kF
getcE		ldaa	#$45		; get the ASCII code of E
		rts
db_keyF	jsr	delay10ms
		brclr	keyboard,$08,getcF
		jmp	scan_r0
getcF		ldaa	#$46		; get the ASCII code of F
		rts
; **************************************************************************
; The following subroutine creates a time delay of 10 ms.
; **************************************************************************
delay10ms 	movb	#$90,TSCR1	; enable TCNT & fast flags clear
		movb	#$06,TSCR2 	; configure prescale factor to 64
		movb	#$01,TIOS	; enable OC0
		ldd 	TCNT
		addd	#3750		; start an output compare operation
		std	TC0		; with 10 ms time delay
wait_lp2	brclr	TFLG1,$01,wait_lp2
		rts