VTech Alphabert s Magic Readport User Manual download pdf (Page 56)

Lab Manual of Microcontroller & Interfacing Page 56

ANL A,#0FH ;Maks Upper Bits Because They Are Not Used

CJNE A,#0FH,REL ;Check Till All Keys Released

AGAIN:

ACALL DELAY

MOV A,P2 ;See If Any Key Pressed Or Not?

ANL A,#0FH ;Mask Upper Bits

CJNE A,#0FH,KPRESS ; If A Is Not Equal To 0fh Then Key Is

; Pressed

SJMP AGAIN ; Check Again If Key Is Not Pressed

KPRESS:

ACALL DELAY

MOV A,P2

ANL A,#0FH ;MASK UNUSED UPPER BITS

CJNE A,#0FH,KPRESS1 ; if a is not equal to 0fh then key is

;pressed

SJMP AGAIN ; CHECK AGAIN IF KEY IS NOT PRESSED

KPRESS1:

MOV P1,#0FEH ; Ground ROW 0

MOV A,P2 ;Read All Columns

ANL A,#0FH ;Mask Unused Upper Bits

CJNE A,0FH,R_0 ;key is pressed in first row (row 0),check

; columns

MOV P1,#0FDH ; Ground ROW 1

MOV A,P2 ;READ ALL COLUMNS

ANL A,#0FH ;MASK UNUSED UPPER BITS

CJNE A,0FH,R_1 ;KEY IS PRESSED IN SECOND ROW (ROW 1),CHECK

; COLUMNS

MOV P1,#0FBH ; Ground ROW 2

MOV A,P2 ;READ ALL COLUMNS

ANL A,#0FH ;MASK UNUSED UPPER BITS

CJNE A,0FH,R_2 ;KEY IS PRESSED IN THIRD ROW (ROW 2),CHECK

; COLUMNS

MOV P1,#0F7H ; Ground ROW 0

MOV A,P2 ;READ ALL COLUMNS

ANL A,#0FH ;MASK UNUSED UPPER BITS

CJNE A,0FH,R_3 ;KEY IS PRESSED IN FOURTH ROW (ROW 3),CHECK

; COLUMNS

LJMP AGAIN

R_0: MOV DPTR,#KCODE0 ;SET DPTR=START OF ROW 0

SJMP CHECK_C

R_1: MOV DPTR,#KCODE1 ;SET DPTR=START OF ROW 1

SJMP CHECK_C

R_2: MOV DPTR,#KCODE2 ;SET DPTR=START OF ROW 2

SJMP CHECK_C

R_3: MOV DPTR,#KCODE3 ;SET DPTR=START OF ROW 3

CHECK_C:

RRC A ;CHECK WHETHER CARRY OCCURS OR NOT

JNC GET_CODE

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VTech Alphabert s Magic Readport User Manual Page 56

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