problem with serial port interfacing

[froten]

Hello,

Im tring to write a program for AT89C51 that can send a stream of one character (which is 5) to the computer, I wrote this program but it doesn't work because I didn't see any signal going out from the Tx pin using the osciloscope. the program is as follows:

mov TMOD,#20
mov TH1,#-3
mov SCON,#50
SETB TR1
AGAIN:
mov a,"5"
acall TRANS
sjmp AGAIN
TRANS:
mov SBUF,a
HERE:
jnb TI,HERE
CLR TI
ret
end

the buad rate should be 9600 bps. I didn't actually connect the circuit to the computer because when I use the osciloscope I don't see any signal on the Tx pin. I have attached both the asm and hex files for more information.

Please any help on this issue is appreciated as it is very important for me to get it working.

 

[budhy]

Try thos code :

   mov   TMOD,#$20
   mov   TH1,#-3
   mov   SCON,#$50
   SETB  TR1
AGAIN:
   mov   a,#"5"
   acall TRANS
   sjmp  AGAIN

TRANS:
   mov SBUF,a
HERE:
   jnb   TI,HERE
   CLR   TI
   ret
   end

 

[froten]

do you think that this code will work as is cost me to reprogram the MCU.

 

[mmohamed15]

what do you mean by it will cost you , r u paying money for programming tha mc?!

 

[budhy]

do you think that this code will work

do you think that this code will not work?

Bassically your code is right, the problem is you don't put the hexadecimal prefix($), and immediate data prefix (#)

Here is the list of mistake you made :

   mov TMOD,#20

the purpose of this instruction is define TIMER1 as mode 2 (auto reload), but without $ prefix this instruction is define TIMER1 as mode 1 (and other TIMER0 setup bits).
It mean you don't have Baudrate Generator for the UART, so the serial port doesn't functioned.

   mov SCON,#50

the same error, cause wrong setup of UART!

 mov a,"5"

mean : move the content of memory number $35 to A

 

[yali]

why you don't use keil and c codes. it will solve a lot of your problems easily