Tech Support Request 032520


Rob Wichterman
Inside Sales Engineer
HMS Networks

Direct: (312) 598-2802




You shouldn’t have to do any of that for RS232:

This is a Modbus RTU application.

Can you please repeat the question and resend any pictures because it looks like the important part of the email didn’t get forwarded to me.

Thank you!

I purchased the Communicator late last year and the plant is just now getting around to get this installed. I am a little confused by the wiring diagram for the RS485. Typically on a half-duplex Modbus RTU application there are only three wires terminated
(RS485+, RS485- & shield). Do I need to terminate the +5V across the resistors shown below or is this done internally?

The last picture is what I have available for terminations on the end device. I do not see a place to terminate the signal ground. Do I just not use this point?




Tim Dykema

Tri-City Engineering & Integration

You shouldn’t have to worry about that termination unless you are getting a lot of errors/noise on the bus. It’s usually only necessary with a longer bus with many devices.

Thanks, I assume you are referring to the signal ground? How about the 5V across resistors? Is that done internally?

Yes it is.