Busy output stays on if resetting communication

automatan

Hi All,

I am working on communicating with two sinamics v20 and one g120 from s7-1200 CB1241 board. I set the modbus related parameters, MB_COMM_LOAD works fine. But, MB_MASTER always busy with no ERROR. In cpu tx and rx is blinking. I am struggling around this. please guide me. thanks.

I have exactly the same problem.

the comms works just fine. but if I interrupt the communications say by turning off the slave and power it back on, the busy output stays on and will not be reset at all.

Please let me know if you can help

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Split from Modbus MB_MASTER block always busy.

Hello,

problem can be in your program logic. Simply test your logic in case of interrupted connection with Slaves, if this will occur your Master must cyclically poll Slaves and refresh without problems communication after reconnect. Give us info.

Update: pls look also to CB properties, there can be defined basic criteria about set end of send/receive conditions.

Thanks for the reply,

I am using two modbus master blocks. the first one only reads the values and the second one is writing. it is always the write block that will cause issues. after restoring the comms link the read block works just fine and the write block stays busy.

i have set a 300ms timeout as well. the request will stay on for at least 1 second so I am sure I don't remove the request in the middle of the process.so when the communication link breaks I expect the timeout error to disengage the block and reset the busy signal. but apparently this not the case...

Hello,

can you pls explain what is that 300ms timeout? What is controlling? Is set by you in code or on HW CP? Simply your logic can work this way, if you loose connection with Slave (expect test with only one Slave f.ex.), your CP must cyclically send requests with defined timeout (1s is enough). If you'll reconnect Slave, it must continue as expected. You can simulate your Slave with PC application and suitable adapter, then you don't need disturb real device and also test in Office.

New question published by _Pavel_ is split to a separate thread with the subject Modbus hangs up.

Best regards
Min_Moderator