PLCnext, Radioline and Modbus RTU
I am experiencing some odd behavior with my AXC 2152 and the implementation of Modbus RTU using the Modbus_RTU_11 library.
I have two PLCs (AXC 2152s) communicating with one another over RAD-900-IFS radios. The radios are operating in the PLC/Modbus RTU dual mode. The PLCs both use SmartElement RS485 modules, and thus, I selected the appropriate block from the library.
I am seeing the message transmit from the master, through the radios, and hit the slave interface. I see the buffer for the module populate with the message bytes, and the block goes busy momentarily, but does not issue a response.
What am I missing in this implementation? It seems as though the slave device is not responding to the poll.
Master Block:
Slave Block:
I have two PLCs (AXC 2152s) communicating with one another over RAD-900-IFS radios. The radios are operating in the PLC/Modbus RTU dual mode. The PLCs both use SmartElement RS485 modules, and thus, I selected the appropriate block from the library.
I am seeing the message transmit from the master, through the radios, and hit the slave interface. I see the buffer for the module populate with the message bytes, and the block goes busy momentarily, but does not issue a response.
What am I missing in this implementation? It seems as though the slave device is not responding to the poll.
Master Block:
Slave Block:
Comments
do the baud rates etc. match ?
What request data are recieved?
Are there anny error messages ?
Maybe try recording the data transfer via the LogicAnalyser.
Also double check the cabling and termination.
For test purpose you could try attaching a PC as either Slave or as Master for easy tests.
kind regards,
Oliver