Hi proffessionals,

We are reading data from a 3rd party device with Modbus TCP communication using CP1243-1 (6GK7 243-1BX30-0XE0)-V3.1 and CPU 1214C DC/DC/DC (CPU 1214C DC/DC/DC)-V4.2. For this we use the ready "MB_CLIENT" block in the library.

The system normally works without any problems. But the communication does not continue when the CPU is de-energized and energized again. When I look at the MB_CLIENT status words, it seems to be sending queries and receiving answers, but the information we read from the 3rd party device does not get. They all show 0. When we energize and de-energize again, the problem continues until I delete the MB_CLIENT block and add a new one, when I fill input and output as before and downlad,  the communication comes back and we read the information.

I will appreciate any suggestions.

Thanks.

frkn001

Hi proffessionals,

We are reading data from a 3rd party device with Modbus TCP communication using CP1243-1 (6GK7 243-1BX30-0XE0)-V3.1 and CPU 1214C DC/DC/DC (CPU 1214C DC/DC/DC)-V4.2. For this we use the ready "MB_CLIENT" block in the library.

The system normally works without any problems. But the communication does not continue when the CPU is de-energized and energized again. When I look at the MB_CLIENT status words, it seems to be sending queries and receiving answers, but the information we read from the 3rd party device does not get. They all show 0. When we energize and de-energize again, the problem continues until I delete the MB_CLIENT block and add a new one, when I fill input and output as before and downlad,  the communication comes back and we read the information.

I will appreciate any suggestions.

Thanks.

A sample program from you may be helpful for volunteers to look into details. 

My guessing to a solution..  Have you tried to force a disconnect? With the PLC switched back on, connect to the server; wait; disconnected. Then connect again. Check the connection status before attempting a request to receive data.

Getting feedback from the control block is essential. You may even use the "Trace" function to record a graph of changing states which may be helpful to diagnose the root problem.

Consider also to look at samples that is available from Siemens which may have some helpful hints. Like this one (How do you program and parameterize Modbus/TCP communication between S7-1500 CPUs and S7-1200 CPUs?).