PIC to PIC interfacing by RS485

fuzzy · Joined: 26 Feb 2005 Posts: 64

Hi,

I'm trying to connect 2 PIC16f876 by rs485 using SN75176 transceiver. I'd like to use half duplex configuration, so i control RE and DE pins togheter by Port C5 that is always 0(receiving). It will be set 1 before transimitting and then it returns to 0.
I use pins C6 and C7 to receive and transmit data.
#use rs232(baud=9600,xmit=PIN_C6,rcv=PIN_C7,enable=PIN_C5,parity=n)

I've some problems in comunication.After a lot of attempt i realized that When one PIC transimts data it seems as it receives what it has transmitted and this will fill in receiving buffer. so the transimitting pic receives the same data it sends. and when the other pic tryes to send data the first pic can't decode data.

I tried all configuration suggested in datasheet to remove bias, with 120 ohm resistors and so on but it's the same. so i should exclude problems on the line.

What will you suggest to try? how can i solve this problem?

thanks!

Mark · Joined: 07 Sep 2003 Posts: 2838 Location: Atlanta, GA

It is because the receive and transmit are on at the same time. Are you sure that you connected them together and there are no shorts.

fuzzy · Joined: 26 Feb 2005 Posts: 64

RE and DE pins are together and they goes high only when PIC transimts.

i'm afraid the pin C5 controlled by software of rs232 goes down before PIC stops transmitting. Is it possible? but I also tryed to force high this pin for a long period during transmission but the problem was the same.

thanks

Ttelmah · Guest

fuzzy · Joined: 26 Feb 2005 Posts: 64

i finally managed it! now my two pic communicate correctly without any fault. i didn't set correctly TRISC. as I set TRISC.7=1 the system began to work!!