Dear Fellows:

I am trying to transmit a number, which I get from keyboard matrix, stored in a location at internal RAM called K_NUM, and now sending it out by using IR LED. The transmission is happening bit by bit but problem I am facing is that on Receiver side, I am using an IR module which normally used in TV etc. This is a small metal box. IT receives the pulse burst (pulse train) and converts this as high signal and no pulse burst converts as low signal. i.e. pulse burst presents = 1
pulse burst not presents = 0.

The actual problem is that I am unable to control the appropriate pulse width. This is important that I want to poll an I/O pin for high and low signal detection at the receiver end, and I would need an accurate pulse width for 1s and 0s.

Please look at the code as follows and if some of you can help me resolving the problem.

TX:
PUSH ACC ; save accumulator to stack
PUSH PSW ; save flags status to stack
CLR C ; clear carry
MOV BIT_CNT,#09h ; load bit_cnt by 8bits +1
MOV A,K_NUM ; load accumulator with key number.
SETB ACC.6 ; set bit 7 of accumulator by 1.

TX_STRT:
DJNZ BIT_CNT,CHK_A7 ; chk if all bit not sent goto next bit.
TX_END:
POP PSW ; other wise prepare to exit, pop PSW
POP ACC ; POP Acc.
AJMP TO_KEY_BRD ; go back to keyboard routin

CHK_A7:
MOV CARR_CNT,#010h ; load burst (pulse train) counter
JNB ACC.7,SND_LO ; if bit7 of acc. is not 1 then goto SND_LO.

SND_HI:
CLR IR_TX ; send low carrier to bit IR_TX
NOP
SETB IR_TX

DJNZ CARR_CNT,SND_HI ; go again if chk if pulse train has completed,
RL A ; rotate accumulator 1 bit left.
AJMP TX_STRT ; goback to start IR tranmit.


SND_LO:
CLR IR_TX ; send low carrier to bit IR_TX
NOP

DJNZ CARR_CNT,SND_LO ; go again if chk if pulse train has completed,
RL A ; rotate accumulator 1 bit left.
AJMP TX_STRT ; goback to start IR tranmit.


END


Thanx a ton

Rauf

microlnk@emirates.net.ae
ardxb@hotmail.com