**********
* Program LOGIC_2 (6811)
*
* Simulates 2 cascaded tens counters.
* Ouputs 00 to 99 in BCD form to LEDs and continually repeats.
*
* Input switches are not used.
*
* P. H. Anderson, MSU, 11 Oct 90; 15 Jan 93
**********

PSCT	EQU  $C000
DSCT	EQU  $D000
IDSCT	EQU  $D300

STACKTP 	EQU  $0045
REG_BASE	EQU  $1000

PORTB	EQU  $04	* output
PORTC	EQU  $03	* input
DDRC	EQU  $07

	ORG PSCT

	LDS #STACKTP
	LDY #REG_BASE

	CLR DDRC,Y	* port c configured as 8-bit input

	CLRA		* zero the counter
L1
	STAA PORTB,Y	* output counter to LEDs
	BSR TIME	* brief delay
	ADDA #$01	* increment counter in decimal manner
	DAA
	BRA L1		* continue

* note that the counter naturally rolls over from $99 to $00

TIME
* subroutine time provides a nominal 0.25 sec delay

	PSHX		* save X on stack

	LDX #50000
DECR
	DEX
	BNE DECR

	PULX		* restore X
	RTS

	ORG DSCT