Hi all
Just deciding using RS-485 fullduplex with
mode 3 serial port(multiprocessor)
The AT89S52 or DS89C450 as slave processor


$INCLUDE (reg_c51.INC)
echo BIT 20H; echo enable bit
TxOK BIT 21H; software flag
org 000h
ljmp begin
org 23h
ljmp serial_IT
/**
* FUNCTION_PURPOSE: This file set up uart in mode 3 (9 bits uart) with
* timer 1 in baud rate generator mode.
* FUNCTION_INPUTS: void
* FUNCTION_OUTPUTS: void
*/
org 0100h
begin:
MOV SCON, #0F0h; /* uart in mode 3 (9 bit), REN=1 */
MOV SADDR,#03h; /* local address */
MOV SADEN,#0FFh; /* address mask */
ORL TMOD, #20h; /* Timer 1 in mode 2 */
MOV TH1, #0FDh; /* 9600 Bds at 11.059MHz */
MOV TL1, #0FDh; /* 9600 Bds at 11.059MHz */
SETB ES; /* Enable serial interrupt*/
SETB EA; /* Enable global interrupt */
SETB TR1; /* Timer 1 run */
loop:
JNB echo,$; /* wait data to echo */
CLR echo ; /* disable echo */
SETB TB8; /* address mode */
SETB TxOK; /* set software flag */
MOV SBUF,#01h; /* send master adress */
JB TxOK,$; /* wait the stop bit transmition */
CLR TB8; /* data mode */
SETB TxOK; /* set software flag */
MOV SBUF,A; /* send data */
JB TxOK,$; /* wait the stop bit transmition */
LJMP loop

;/**
; * FUNCTION_PURPOSE: serial interrupt, echo receive data to master
; * FUNCTION_INPUTS: P3.0(RXD) serial input
; * FUNCTION_OUTPUTS: none
; */
serial_IT:
JNB TI,END_Test_TI; /* if reception occur */
CLR TI; /* clear transmition flag for next transmition
*/
CLR TxOK; /* clear software transmition flag */
END_Test_TI:
JNB RI,END_Test_RI; /* test if it is a reception */
CLR RI; /* clear reception flag for next reception */
JNB RB8,address_mode
CLR SM2; /* go into data mode */
LJMP END_Test_RB8
address_mode:
MOV A,SBUF; /* Read receive data */
SETB SM2; /* return into address mode after receive data */
SETB echo
END_Test_RB8:
END_Test_RI:
RETI
end

from Atmel uart application note


Is the code above for fullduplex slave?

Thank's
JBJ