AnsweredAssumed Answered

ADM2587E - Problems communicating over short distances at high Baud Rates

Question asked by ellisplace on Feb 7, 2012
Latest reply on Mar 6, 2012 by ConalW

Hello

 

We use the ADM2587E in our current product design. We have noticed intermittent RS485 errors when communicating at high baud rates (115200), over short distances (<2m) with no termination resistor present.

 

In production our devices always operate with a 120R termination resistor at each extreme, but in isolation it would be expected that an individual device should communicate without the need for a termination resistor. Below is the circuit diagram for our 485 interface.

 

RS485 CIRCUITRY.bmp

Below are the scope readings for the A-B signal firstly with no termination, and with 120R termination.

F0017TEK.BMP  F0020TEK.BMP

 

Notice the double dip at the start of every returned message.

tek00003.png

 

This does not appear on the previous design (shown below without termination), or when 120R termination is used.

tek00002.png

 

Thanks for any help you can offer.

Regards

Ellis

Outcomes