Hi Rauf,

Try to change your program as following

TX: PUSH ACC ;For what?
PUSH PSW ;For what?
MOV BIT_CNT,#08H ;TO SEND 8 BITS
MOV A,K_NUM ;load accumulator with key number.
SETB ACC.7 ;FIRST BIT IS ALWAYS 1
CLR IR_TX ;TO BE ON THE SAFE SIDE
TX_STRT: RL A ;rotate accumulator 1 bit left.
MOV CARR_CNT,#010h ;load burst (pulse train) counter
TX_BIT: MOV IR_TX,C ;WE SEND PRESENT BIT
NOP ;WIDTH OF BIT
CLR IR_TX ;END OF PRESENT BIT
DJNZ CARR_CNT,TX_BIT ;IS BURST OVER?
DJNZ BIT_CNT,TX_STRT ;chk if all bit not sent goto next bit.
TX_END: POP PSW ;For what?
POP ACC ;For what?
JMP TO_KEY_BRD ;go back to keyboard routin
END

I hope it helps you greatly. Please inform me do you got the success or not

Good luck,

George