ORG 0			/*PROGRAM START VECTOR*/
JMP main

ORG 0003H		/*EXTERNAL INT1 START VECTOR*/
JMP runKeyISR

/************************************************************************
*Program to scan a keypad on P1 and output the pressed kay value to P0	*
*P1.0 - P1.3 rows		P1.4 - P1.7 columns			*
*Process key flag = 4OH							*
************************************************************************/

ORG 0030H		/* MAIN START VECTOR*/

main:
	MOV TMOD, #01H 	/*SET T0 FOR 16 BIT TIMER*/
	SETB IT0 	/*SET EX0 AS EDGE ACTIVATED*/
	SETB EX0 	/*SET EXTERNAL KEY PRESS INT*/
	CLR P1.0 	/*SET ROWS AS OUTPUTS FOR SCAN*/
	CLR P1.1
	CLR P1.2
	CLR P1.3
	SETB P0.4	/*SET COLUMNS AS INPUTS FOR SCAN*/
	SETB P1.5
	SETB P1.6 	
	SETB P1.7
loop:	SETB EA 	/*ENABLE INTS*/
	JNB 40H, $	/*WAIT FOR KEY DOWN INT IF NO KEY FOUND YET*/		
	CLR 40H		/*CLEAR PROCESS KEY FLAG*/
	MOV P0, A	/*MOVE SCANNED NUMBER FROM A TO P0*/
	JMP loop	/*JUMP BACK TO WAITING FOR KEY DOWN*/


runKeyISR:
	CLR EX0 	/*DISABLE INT0 INT*/
	CALL debounce	/*RUN DELAY TO CANCEL OUT DEBOUNCE*/
	CALL scanPad	/*GET KEY DOWN NUMBER*/
	CALL clearPad 	/*IN PLACE OF waitForKeyRelease*/
	CLR IE0 	/*CLR INT0 FLAG*/
	SETB EX0 	/*ENABLE INT0 INT*/
	CLR EA		/*DISABLE INTS*/
	RETI

debounce:
	CLR TR0		/*STOP TIMER IN CASE ITS LEFT RUNNING*/
	MOV TH0, #8AH	/*SET TIMER0 FOR 35,536 (8AD0)*/
	MOV TL0, #0D0H 	
	SETB TR0 	/*START TIMER*/
	JNB TF0, $ 	/* WAIT FOR OVERFLOW*/
	CLR TF0 	/*CLEAR OVERFLOW*/
	CLR TR0 	/*STOP TIMER0*/
	RET

scanPad:
	MOV A,0H	/*CLEAR A READY FOR NEW KEY DOWN NUMBER*/
	CLR P1.0	/*CLEAR 1ST ROW*/
	SETB P1.1	/*SET ALL OTHER ROWS*/
	SETB P1.2
	SETB P1.3
	CALL colScan	/*SCAN THE COLUMNS*/
	JB 40H, return	/*TEST FOR KEY*/
	SETB P1.0
	CLR P1.1	/*CLEAR 2ND ROW*/
	SETB P1.2	/*SET ALL OTHER ROWS*/
	SETB P1.3
	CALL colScan 	/*SCAN THE COLUMNS*/
	JB 40H, return	/*TEST FOR KEY*/
	SETB P1.0
	SETB P1.1
	CLR P1.2	/*CLEAR 3RD ROW*/
	SETB P1.3	/*SET ALL OTHER ROWS*/
	CALL colScan 	/*SCAN COLUMNS*/
	JB 40H, return	/*TEST FOR KEY*/
	SETB P1.0	/*SET ALL OTHER ROWS*/
	SETB P1.1
	SETB P1.2
	CLR P1.3	/*CLEAR 4TH ROW*/	
	CALL colScan 	/*SCAN COLUMNS*/
return:	RET

colScan:
	JNB P1.4, skip	/*SCAN FIRST COLUNM*/
	INC A		/*INC A FOR KEY ID*/
	JNB P1.5, skip	/*SCAN SECOND COLUMN*/
	INC A		/*INC A FOR KEY ID*/
	JNB P1.6, skip	/*SCAN THIRD COLUNM*/
	INC A		/*INC A FOR KEY ID*/
	JNB P1.7, skip	/*SCAN FOURTH COLUMN*/
	INC A		/*INC A FOR KEY ID*/
	RET		/*RETURN IF NO KEY FOUND ON THAT COLUMN*/
skip:	SETB 40H 	/*KEY FOUND SO SET TO JUMP OUT OF JNB WAIT LOOP*/
	RET

clearPad:
	CLR P1.0	/*CLEAR THE KEYPAD ROWS READY FOR NEXT SCAN*/
	CLR P1.1
	CLR P1.2
	CLR P1.3
	RET


END