#include "c:\miniide\hcs12.inc"
		org	$1000
count		ds.b	1		; OC0 match count
oc0cnt          ds.b    1
		org	$2000		; start of program
		lds	#$2000		; set up stack pointer
		movb	#$FF,ddrb	; configure port B for output
		clr	count
		movb	count,portb
		movb	#$90,tscr1	; enable tcnt and fast timer flag clear
		movb	#$06,tscr2	; set TCNT prescaler to 128, enable timer reset
		bset	tios,OC0	; enable OC7
		ldd	tcnt		; start an OC0 operation
		addd    #60000          ;       "
		std     tc0             ;       "
		movb	#$01,tflg1	; clear C0F flag
		bset	tie,C0I		; enable OC0 match interrupt
		movb    #25,oc0cnt
		cli			; enable maskable interrupt
forever		nop
		tst     oc0cnt
		beq     reset_it
		bra	forever
reset_it	movb    #25,oc0cnt      ; quarter second expired,
		inc     count           ; increment oc0 count
		movb    count,portb     ; update LED displays
		bra     forever
		
oc0_ISR         ldd     tc0             ; start a new OC0 operation and
		addd    #60000          ; also clear the OC0 flag
		std     tc0             ;       "
		dec     oc0cnt
		movb    #$FF,portb
		rti
		org     $3E6E
		fdb     oc0_ISR
		end