Internet PLC Forum

General => Technical support => Topic started by: ccdubs on August 01, 2014, 04:42:34 PM

Title: Maximum PLC ID for Modbus RTU
Post by: ccdubs on August 01, 2014, 04:42:34 PM

I remember reading before that the PLC ID's were only valid up to a limit when using MODBUS RTU. I can't find this reference anymore, could you please confirm what this?

Thanks

Title: Re:Maximum PLC ID for Modbus RTU
Post by: support on August 01, 2014, 11:57:49 PM

According to Modbus specifications the ID for a Modbus slave may only be between 1 and 247.

Title: Re:Maximum PLC ID for Modbus RTU
Post by: EDGAR on August 02, 2014, 08:00:25 AM

Hi, and agreed!

You might be able to handle that many devices. However, if you are using RS-485 network,  the RS-485 transceivers may not be capable of driving that many devices in the same network. See http://www.modbus.org/ also see http://en.wikipedia.org/wiki/RS-485 for bias network termination and other details.

Ed