Hello All,

I have written a program which has the functunality that when a switch is pressed one LED becomes ON and remains on ...
and when the same switch is again pressed the same LED gets OFF ...

The program is not working properly ... could any one help me out where the progarm is lacking ...

DELAY is 65 MS ... timer 1

;***************************************************************
DELAY_HIGH EQU 003H
DELAY_LOW EQU 018H
FLAG_FIRST EQU 031H
FLAG_SECOND EQU 032H
FLAG_INVALIDKEY EQU 033H
FLAG_ALTER EQU 034H
NEWKEY EQU 034H

ORG 000H
MOV SP,#050H
SJMP START

ORG 001BH
INTERRUPT_1:
PUSH ACC
PUSH PSW
CLR TR1
MOV PSW,#00H
ACALL KEYPRESSED
JNZ CALCULATE
JB FLAG_SECOND,HALT1 ; if no key is pressed and earlier the key were presed taking into
JB FLAG_FIRST,COOL ;account the 1st & 2nd press, then jump to HALT1 and only once key
JMP AGAIN ;is pressed then jump to COOL or jump to AGAIN

CALCULATE:
ACALL KEYPRESSED ; again check whether any key is pressed or not
JZ HALT ;if no key is pressed then jump to halt for checking the key is pressed ;before or not by cheking the flag ... FLAG_FIRST
ACALL CONVERT ;check the validity of the key pressed
JBC FLAG_INVALIDKEY,HALT; if the key pressed is invalid then jump to HALT
INC R0 ;increment R0 fro checking whether the key is pressed first time or not
CJNE R0,#01,COMPARE ;if the key is not pressed for the first time then jump to COMPARE
MOV NEWKEY,A ;here it shows the key is pressed for the first time and so the fresh key ;is taken to a new flag named NEWKEY for further checking on ;second time key hit
SETB FLAG_FIRST ;set this flag which shows the key is pressed 1st time, this flag is used ;while the checking the in the subroutine HALT
JMP OUTPUT ; jump to output the 1st time keypressed

COMPARE:
CJNE A,NEWKEY,HALT ;if the key is kept pressed or the second time is pressed is not the ;same key then jump to HALT
JB FLAG_ALTER,RUN ;If after the 1st time key pressed is released then FLAG_ALTER is set ;and checked here whether the condition is true or not
JMP OUTPUT ;jump to output for the 1st time key pressed
RUN:
SETB FLAG_SECOND ;this flag indicated that the key is pressed 2nd time
JMP OFF ;so jump to OFF

OUTPUT:
MOV P2,A ;output the value of A to the LED's
JMP AGAIN ;jump to AGAIN subroutien
OFF:
MOV P2,#00H ;make the LED off
JMP AGAIN ;jump to AGAIN

COOL:
SETB FLAG_ALTER ;if there is no key is pressed but a key is pressed for the 1st time before
MOV P2,NEWKEY ;then FLAG_ALTEr shows that the key next that will be pressed is ;being pressed second time and so the FLAG_SECOND flag should be ;set accordingly ahead in the program
JMP AGAIN

HALT:
JB FLAG_FIRST,AGAIN ;this flag shows that previously a key is pressed for the 1st time so the ;previuos conditions should be preserved otherwise the a fresh ;counting is taken into account
HALT1:
CLR FLAG_FIRST ;all the flags are cleared for a new key to be pressed
CLR FLAG_SECOND
CLR FLAG_ALTER
CLR NEWKEY
MOV P2,#00H
MOV R0,#00
AGAIN:
ACALL TIMER_1
POP PSW
POP ACC
RETI

KEYPRESSED:
MOV A,P1
CPL A
RET

START:
MOV IE,#088H
MOV TMOD,#010H
MOV P1,#0FFH
MOV P2,#00H
MOV R0,#00H
MOV R7,#00H
CLR FLAG_FIRST
CLR FLAG_SECOND
ACALL TIMER_1

KEY:
INC R7
JMP KEY

TIMER_1:
MOV TL1,#DELAY_LOW
MOV TH1,#DELAY_HIGH
SETB TR1
RET

CONVERT:
CLR FLAG_INVALIDKEY

CJNE A,#01H,SECOND
RET
SECOND:
CJNE A,#02H,THIRD
RET
THIRD:
CJNE A,#04H,FOURTH
RET

FOURTH:
CJNE A,#08H,FIVE
RET
FIVE:
CJNE A,#010H,SIX
RET
SIX:
CJNE A,#020H,SEVEN
RET
SEVEN:
CJNE A,#040H,EIGHT
RET
EIGHT:
CJNE A,#080H,BAD
RET
BAD:
SETB FLAG_INVALIDKEY
RET

END
;***************************************************************

Arvind Shrivastava ...