SBC6303+SBC-I/O 6821 port test program

sbcio21.asm

*	SBCIO21 - 6821 PORT TEST PROGRAM
*	TARGET: LILBUG ON SBC6303
*	ASSEMBLER: ARCPIT X6801.EXE
*
*	6821 RESISTERS
PORTA	EQU	$8050	A,PORT/DIRECTION
CRA	EQU	$8051	A,CONTROL
PORTB	EQU	$8052	B,PORT/DIRECTION
CRB	EQU	$8053	B,CONTROL
*
*	LILBUG INTERNAL ROUTINE
DELAY	EQU	$F8D8 54MS DELAY
MAIN	EQU	$F952
*
*	INITIALIZE
	ORG	$0080
	CLR	CRB	SELECT DIRECTION
	LDAA	#$FF	OUTPUT CODE
	STAA	PORTB	SET OUTPUT
	LDAA	#$04	PORT CODE
	STAA	CRB	SELECT PORT
*
*	START
	LDAA	#10
LOOP1	COM	PORTB	REVERSE PORT
	LDAB	#10
LOOP2	JSR	DELAY
	DECB
	BNE	LOOP2
	DECA
	BNE	LOOP1
	JMP	MAIN
*
        END