To avoid these types of problems, I recommend changing to UDP with a watchdog and time-of-day added to the data being sent / received.  In this way, both PLCs know when the last valid communication was from the other PLC and can act accordingly.

UDP is blind and assumes the other device receives.  In this way, it does not fault the connection (which you have to monitor and restart automatically upon failure for other protocols) if the remote device goes offline.

MRCordova

viki_bum

Thanks a lot..

Actually I am triggering the controller for exchange of data. Its on modbus.

As soon as the controller misbehaves data stops updating i have checked in software polling bits are proper.

but data transfer is not proper.

Regards
Vikki

Hi, i'm having a very similar problem, i have a PLC S7-1200 as "master" in a Modbus TCP/IP Network, and i have another PLC s7-1200 as "slave", the first PLC is like 10 Km away from the second, i have antennas to build the network, so i can see the two PLC in a LAN network (i connect my PG in any switch of the network and i can see everything, and i can download the projects in all the plc with tia portal) i use MB_CLIENT and MB_SERVER Blocks, everything works fine, until we have a major problem of communication as 2 Hr with out energy in my antennas,  the master PLC now is incompatible device (I cant see it with TIA portal 15 it says incompatible device, I cant see it with my WinCC runtime, I cant see it with web server, i cant see it with my other PLC) But it don't go to STOP state, is runing, only all the communications fail, the only way to reestablish all is turn off the power of the master PLC then turn ON, and everything solves, then i check the diagnostic buffer and only register the lack of energy, but no other event.

I have other project but with 13 PLC as slave, and one central PLC and it happen the same thing.

In the same project in the past, i done first the communication with Tsend, TRecive, Tcon instruction but it happend the same thing

I'm thinking to do the hardware restart when i stop getting response from the other PLC in some time , but there is a way to solve this problem with out doing that?.

Thanks.

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Split from How to do warm restart S7 300 plc by program.