Modbus RTU addressing - No Raspberry Pi

A

andy@fm

New member
Set up is two four relay / 4 input V4.0 boards with no jumpers on the first board and the second board has the RS485 terminator and ID0 jumpers fitted.

I am using Qmodmaster to control the boards.

I am able to turn on and read the coil status from a single board, but when I attached the second board I get check sum errors and the relay on the second board mirrors the relay status of the first.

I also tried running Modpoll to scan. That also only sees one device and then gives "Illegal Data Address exception response!"

Is there anything else I need to configure ?
 
alexburcea

alexburcea

Moderator
Staff member
Hi,

Please connect just one card and place the address jumpers in various configurations and see what addresses are set. Looks like your second card does not change the Modbus address. Please do a power cycle after you change the jumpers so the address actually update.
 
A

andy@fm

New member
So with a single board attached it only communicates with address 1 no matter which jumpers are added. I always change the jumpers with the power off.
 
alexburcea

alexburcea

Moderator
Staff member
One shortcut is to connect one of the card to the raspberry and change the address offset , check the "cfg485wr" command.
We will investigate this and if is the case will came with a firmware update.
It will help if you can test the jumpers on both cards.
 
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