Dear all,

I have come across another problem, and it seems I'm running out of ideas on where the problem lies.

I am using AT89S51. My project is to received a stream of data via RS485 and select the specified data as the station number of each uC.

Now, I'm just testing the serial port ... And I keep on finding as is my serial port does not work as I wanted ...

As I keep on trying to sort out all possibilities. I'm using this code bellow. The idea of this code is the uC keeps on sending the Acc that was read from P1 and outputs the value to P2. And if I short the Tx and Rx port of the uC, then I should received the same data that I was sending out. To prove that I have received the data, I swaped the Acc and output it to P2.
The P0.0 is for giving pulse to P0.0 (MAX1232) as my reset generator.

Here is my code :

$MOD51
org 0000H
ljmp INITIAL

org 0100H
INITIAL:
setb P0.0
mov TH1,#0FDH
mov TMOD,#20H
setb TR1
clr P0.0
mov PCON,#00H
mov SCON,#0D0H
clr TI
clr RI
MULAI:
setb P0.0
mov A,P1
mov P2,A
mov SBUF,A
clr P0.0
clr TI
jb RI,SERIAL_RECEIVED
ljmp MULAI

org 0150H
SERIAL_RECEIVED:
clr P0.0
mov A,SBUF
swap A
setb P0.0
mov P2,A
jmp SERIAL_RECEIVED

And ... I'm stuck ... My code keeps on running as if it does not reads the Rx even I have short the Tx and Rx port ...
Any idea ??? Please ...