ORG $100
	
	 DC.L ISR
CRA  EQU $52003
CRB  EQU $52007
DDRA EQU $52001
DDRB EQU $52005
PDRA EQU $52001
PDRB EQU $52005

   	ORG $900
	
	BCLR.B #2,CRA		;set to choose DDRA
	BCLR.B #2,CRB		;set to choose DDRB
	
	MOVE.B #00,DDRA		;set PA0 to PA7 as inputs
	MOVE.B #$FF,DDRB	;set PB0 to PB7 as outputs

	BSET.B #0,CRA		;enable CA1 interrupt
	BSET.B #3,CRB		;set CRB to pulse mode 101
	BCLR.B #4,CRB		
	BSET.B #5,CRB		

	BSET.B #2,CRA		;set to choose PDRA
	BSET.B #2,CRB		;Set to choose PDRB
	
	MOVE.B	#$07,CRA
	MOVE.B	#$2C,CRB     
	MOVE.B 	$52001,D0
	ANDI.W	#$F8FF,SR	;set interrupt level to 0

LOOP 	
    MOVE.B #247,D7	    ;input single character
    TRAP #14		
	MOVE.B D0,PDRB
	BRA LOOP

	ORG $1800
	
ISR	MOVEM.L D0-D7/A0-A6,-(A7)	;store the regitsers to the stack
	MOVE.B PDRA,D0		
	MOVE.B #248,D7              ;output single character
	TRAP #14			
	MOVEM.L (A7)+,D0-D7/A0-A6	;restore the registers
	RTE				            ;return from exception