HI  experts

        i am working with plc controller s7 1200 and  modbus communication module is cb1241.i communicating plc controlller to micro controller and it is third party .i had read data from microcontroller to plc and it is fine but  now i got problem with writing data to microntroller. i didt understand  writing operation .i just tried with modbus master block and  mode i put is one and write data given through move block.but it is not working

my doubt is

1,micro controller accepting data as eight bit (that is MSB and LSB) how to send data from plc to microcontroller as MSB and LSB

please give some configuration details

2,please give some broad detail about modbus rtu write operation

3,how we can check plc controller is  sending data to micro controller without connecting micro controller

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Split from S7-1200 MODBUS problem with third-party device.

jhon benil

....i just tried with modbus master block and  mode i put is one and write data given through move block.but it is not working.....

 Hi!

If your modbus functions are correctly written in the microcontroller (and I assume that they are, since you can read data out of it) then you should be able to write data from the PLC (master) to the microcontroller (slave), but not with MOVE blocks.

Check out the TIA help of the MB_MASTER block, there is an example how to use it for writing. There is also a table with the DATA_ADDR values.