Part 1 - Keypad Scanning

start:
	MOV R0, #0 ; clear R0 - the first key is key0
; scan row0
	SETB P0.3 ; set row3
	CLR P0.0 ; clear row0
	CALL colScan ; call column-scan subroutine
	JB F0, finish ; | if F0 is set, jump to end of program
		; | (because the pressed key was found and its number
		; is in R0)

; scan row1
	SETB P0.0 ; set row0
	CLR P0.1 ; clear row1
	CALL colScan ; call column-scan subroutine
	JB F0, finish ; | if F0 is set, jump to end of program
		; | (because the pressed key was found and its number
		; is in R0)

; scan row2
	SETB P0.1 ; set row1
	CLR P0.2 ; clear row2
	CALL colScan ; call column-scan subroutine
	JB F0, finish ; | if F0 is set, jump to end of program
		; | (because the pressed key was found and its number
		; is in R0)

; scan row3
	SETB P0.2 ; set row2
	CLR P0.3 ; clear row3
	CALL colScan ; call column-scan subroutine
	JB F0, finish ; | if F0 is set, jump to end of program
		; | (because the pressed key was found and its number
		; is in R0)
	JMP start ; | go back to scan row 0
		; | (this is why row3 is set at the start of the
		; program
		; | - when the program jumps back to start, row3 has
		; just been scanned)

finish:
	JMP $ ; program execution arrives here when key is found – do
		; nothing

; column-scan subroutine
colScan:
	JNB P0.4, gotKey ; if col0 is cleared - key found
	INC R0 ; otherwise move to next key
	JNB P0.5, gotKey ; if col1 is cleared - key found
	INC R0 ; otherwise move to next key
	JNB P0.6, gotKey ; if col2 is cleared - key found
	INC R0 ; otherwise move to next key
	RET ; return from subroutine - key not found
gotKey:
	SETB F0 ; key found - set F0
	RET ; and return from subroutine

Part 2 - Data Transmission through Keypad

start:
	MOV R0, #0 ; clear R0 - the first key is key0
; scan row0
	SETB P0.3 ; set row3
	CLR P0.0 ; clear row0
	CALL colScan ; call column-scan subroutine
	JB F0, finish ; | if F0 is set, jump to end of program
		; | (because the pressed key was found and its number
		; is in R0)

; scan row1
	SETB P0.0 ; set row0
	CLR P0.1 ; clear row1
	CALL colScan ; call column-scan subroutine
	JB F0, finish ; | if F0 is set, jump to end of program
		; | (because the pressed key was found and its number
		; is in R0)

; scan row2
	SETB P0.1 ; set row1
	CLR P0.2 ; clear row2
	CALL colScan ; call column-scan subroutine
	JB F0, finish ; | if F0 is set, jump to end of program
		; | (because the pressed key was found and its number
		; is in R0)

; scan row3
	SETB P0.2 ; set row2
	CLR P0.3 ; clear row3
	CALL colScan ; call column-scan subroutine
	JB F0, finish ; | if F0 is set, jump to end of program
		; | (because the pressed key was found and its number
		; is in R0)
	JMP start ; | go back to scan row 0
		; | (this is why row3 is set at the start of the
		; program
		; | - when the program jumps back to start, row3 has
		; just been scanned)

finish:
	JMP start ; program execution arrives here when key is found – do
		; nothing

; column-scan subroutine
colScan:
	JNB P0.4, gotKey ; if col0 is cleared - key found
	INC R0 ; otherwise move to next key
	JNB P0.5, gotKey ; if col1 is cleared - key found
	INC R0 ; otherwise move to next key
	JNB P0.6, gotKey ; if col2 is cleared - key found
	INC R0 ; otherwise move to next key
	RET ; return from subroutine - key not found
gotKey:
	SETB F0 ; key found - set F0
	MOV A, R0
	MOV P1, A
	MOV R0, #0
	CLR F0
	RET ; and return from subroutine

Laboratory Report: Click here to download the file