Need Help with RS485..

[eidtech]

Hi Forum...

I have a problem with RS485...

I'm programming an AVR Microcontroller to communicate with 2 RS485 Equipment.

At beginning of code execution all is fine... but after some minutes(3-5) MCU starts to receive corrupted data (seen in Oscilloscope and forwarded to other RS232 Terminal), by example the same data but in different order (random), duplicated bytes, etc.

I've tried with some RS485 Converters (from Home Made to Commercial converters). Trying: Optocoupled, NonOptocoupled, Using Terminate Resistor (120 Ohm), Line Resistors (in Series with A & B - 47 Ohms), Pulling Down and Pulling Up Resistors in A & B (560 Ohms).

When 120 Ohms Resistor was connected the problem was reduced but still present now.

Any idea to solve my problem?

Thank u very much to all.

 

[dkace]

Have you tried HUGE zenner diodes ?
D.

 

[IanP]

And who is the master? or does this network have more than one master?

Regards,
IanP

 

[artem]

eidtechm, that means your problem lies in your program.
If you do not trust your rs485 line driver - get a 2 PC and put 2 converters in duplex mode then check the communication by hyperterminal or similar .

 

[bohumilfulin]

put some delay between tx and rx state.

 

[jayavardhan]

without knowing the hardware connections you gave and about the number of masters and number of slaves we can't solve the problem.

 

[Bassem_fahmy]

try putting a single pull up and pull donw resistors that force the levels in the safe range