hi all,
I hav written one code for interfacing 4X4 matrix keypad which is as follows;
;Keyboard subroutine. This program sends the ASCII code
;for pressed key to P0
;P1.0-P1.3 connected to rows, P2.0-P2.3 connected to columns
.ORG 0000H
MOV P2,#0FFH ;make P2 an input port
K1: MOV P1,#0 ;ground all rows at once
MOV A,P2 ;read all col. (ensure all keys open)
ANL A,00001111B ;masked unused bits
CJNE A,#00001111B,K1 ;check til all keys released
K2: ACALL TIME
ACALL DELAY ;call 20 msec delay
MOV A,P2 ;see if any key is pressed
ANL A,#00001111B ;mask unused bits
CJNE A,#00001111B,OVER ;key pressed, await closure
SJMP K2 ;check il key pressed
OVER: ACALL TIME
ACALL DELAY ;wait 20 msec debounce time
MOV A,P2 ;check key closure
ANL A,#00001111B ;mask unused bits
CJNE A,#00001111B,OVER1;key pressed, find row
SJMP K2 ;if none, keep polling
OVER1: MOV P1,#11111110B ;ground row 0
MOV A,P2 ;read all columns
ANL A,#00001111B ;mask unused bits
CJNE A,#00001111B,ROW_0;key row 0, find the col.
MOV P1,#11111101B ;ground row 1
MOV A,P2 ;read all columns
ANL A,#00001111B ;mask unused bits
CJNE A,#00001111B,ROW_1;keyrow 1, find the col.
MOV P1,#11111011B ;ground row 2
MOV A,P2 ;read all columns
ANL A,#00001111B ;mask unused bits
CJNE A,#00001111B,ROW_2;key row 2, find the col.
MOV P1,#11110111B ;ground row 3
MOV A,P2 ;read all columns
ANL A,#00001111B ;mask unused bits
CJNE A,#00001111B,ROW_3;keyrow 3, find the col.
LJMP K2 ;if none, false input, repeat
ROW_0: MOV DPTR,#KCODE0 ;set DPTR=start of row 0
SJMP FIND ;find col. key belongs to
ROW_1: MOV DPTR,#KCODE1 ;set DPTR=start of row 1
SJMP FIND ;find col. key belongs to
ROW_2: MOV DPTR,#KCODE2 ;set DPTR=start of row 2
SJMP FIND ;find col. key belongs to
ROW_3: MOV DPTR,#KCODE3 ;set DPTR=start of row 3
FIND: RRC A ;see if any CY bit low
JNC MATCH ;if zero, get the ASCII code
INC DPTR ;point to next col. address
SJMP FIND ;keep searching
MATCH: CLR A ;set A=0 (match is found)
MOVC A,@A+DPTR ;get ASCII code from table
MOV P0,A ;display pressed key
LJMP K1
TIME: MOV TMOD,#01
MOV TL0,#0FEH
MOV TH0,#0B7H
RET
DELAY: SETB TR0
AGAIN: JNB TF0,AGAIN
CLR TR0
CLR TF0
RET

;ASCII LOOK-UP TABLE FOR EACH ROW
.ORG 3000H
KCODE0: DB 'A','9','8','7' ;ROW 0
KCODE1: DB 'B','6','5','4' ;ROW 1
KCODE2: DB 'C','3','2','1' ;ROW 2
KCODE3: DB 'D','#','0','*' ;ROW 3
.END

After assembling the code i m getting erros as "Undefined opcode" for the 4-lines of look up table. I m not able to correct my mistakes. so plz can anybody help me out to correct these errors. Also tel me what mistake is been done exactly.
Waiting for reply.

Pritam