Hi Experts,

We've successfully communicated Yokogawa and S7-200 thru Modbus RTU, however communication timeouts every after an hour. We restore the communication by switching off and on the S7-200 PLC but it still occur, every after an hour it timeouts. We did several troubleshooting like isolating the Yokogawa system to S7-200 PLC in order to determine which one causes the timeout error. This time we disconnected our modbus cable to Yokogawa Modbus module and connect it to our laptop and use Modscan instead. Same problem occurs, after an hour of good communication, it timeouts after an hour.

Need your expert opinion what could be the problem. Please refer to attached pictures for the timeout error. First picture shows while the PLC communication is ok. Second picture shows after timeout error occur. Thank you in advanced.

PLC used is S7-200 CPU 226.

Notice how MBUS_SLAVE Error output MB2 displays value of 10 after an hour. Don't know why this happens every after an hour. Anyone give opinion what could be wrong with the program? 

Hi,

Error code 10 (MB10)  means "Slave function not enabled"

All i can say is that somehow freeport is not enabled (SM30.0) OR "ModbusActive" value got altered after MMUS_INIT (See Symbol Table -> Library -> Modbus Slave and monitor the value)

But because SMB30 (MODE=1) and "ModbusActive" are set in INIT and read in SLAVE in the next network, this can not be the issue.

Maybe something else in the program causing a hick up preventing MBUS_INIT to enable free-port due to a send or receive timeout else where?