/************************************************************************************/
// PROGRAM TO DEMONSTRATE 4x4 keyboard interfacing
/************************************************************************************/
ORG 0000H
/************************************************************************************/
/* I/O PIN INITIALISATIONS AND DECLARATIONS */
/************************************************************************************/
C1 EQU P2.0
C2 EQU P2.1
C3 EQU P2.2
C4 EQU P2.3
ROW1 EQU P2.4
ROW2 EQU P2.5
ROW3 EQU P2.6
ROW4 EQU P2.7
MOV P2,#00H
MOV P0,#00H
MOV DPTR,#MSG
CLR A
MOV B,#00H
MOV R3,#00H
MOV SCON,#50H
MOV TMOD,#20H
MOV TH1,#0FDH
SETB TR1
/************************************************************************************/
/* READING COLUMN VALUE */
/************************************************************************************/
AGAIN: ACALL DELAY
MOV P2, #0FH
ACALL DELAY
K1: MOV A,P2
CJNE A,#0FH,KK1
SJMP K1
KK1: JB C1,N1
MOV B,#00h
ACALL DELAY
N1: JB C2,N2
MOV B,#01h
ACALL DELAY
N2: JB C3,N3
MOV B,#02h
ACALL DELAY
N3: JB C4,N4
MOV B,#03h
ACALL DELAY
/************************************************************************************/
/* READING ROW VALUE */
/************************************************************************************/
N4: MOV P2, #0F0H
K11: MOV A,P2
CJNE A,#0F0H,KK11
SJMP K11
KK11: ACALL DELAY
JB ROW1,NR1
MOV R3,#00h
ACALL DELAY
NR1: JB ROW2,NR2
MOV R3,#04h
ACALL DELAY
NR2: JB ROW3,NR3
MOV R3,#08h
ACALL DELAY
NR3: JB ROW4,NR4
MOV R3,#0Ch
ACALL DELAY
NR4: MOV A,R3
/************************************************************************************/
/* SENDING KEYVALUE TO PORT 0 AND SERAIL PORT */
/************************************************************************************/
ADD A,B
MOV P0,A
MOVC A,@A+DPTR
MOV SBUF,A
AGAIN_SR:JNB TI,AGAIN_SR
CLR A
SJMP AGAIN
/************************************************************************************/
/* DELAY SUBROUTINE */
/************************************************************************************/
DELAY: MOV R6,#5FH
a1: MOV R5,#0FEH
a2: DJNZ R5,a2
DJNZ R6,a1
RET
/************************************************************************************/
/* LOOKUP TABLE W.R.T 0-15 SWITCHES IN HEX KEYPAD */
/************************************************************************************/
MSG: DB '0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F',0
