Dear all,

I came accross unusual problem.

Et200SP CM PtP (fw.1.0.2) is on the bus with slave RS485 device No. 2

Every time the FB : Modbus_maser reqests for respond form no.2, the FB (PtP) stops working. However after adding PC (232/485 converter) as slave device no 3, I can get all respond from no.2. In short, it looks that converter makes the bus working, when is supplied and not set to listening it is still working. After removing converter or switch off connection goes down to. If the converter is not connected, the CM PtP behaves as it was disconeccted from bus.

There is termination on slave no.2 (120ohm) and on CM PtP (330ohm).

Is it possible that I need to pull up the Tx and Rx?

hi,

could you share a scretch of your wring? I think it´s easier to understand then.

regards,

[Solved] - Solution ->

For the slave device  the difference of potential between the A(+) and B(-) terminals must be of at least 0,2 V.

Terminator bridge with supply form V20 did the job.

Does anyone know why Et200SP CM PtP is not providing such voltage difference in idle or listening?