Modbus RTU communication between SlimLine & Toshiba VF-AS1

[Anonimo]

Hello everybody! I’m trying to make a modbus communication between slimline MPS046B100 CPU and an inverter Toshiba VF-AS1. I used the ModbusMaster FB and i’ve parametered everything following the example given in the manual trying to adapt everything with the inverter parameters but unfortunately i’m having a problem in the reception of the answer.

The SysGetLastError function returns the error 10007506, error receiving the answer frame (Wrong character, wrong length, wron CRC). Can anyone please give me some assistance (here’s the screenshot of the function i’ve made).

[Sergio Bertana]

It seems that the inverter doesn’t answer to the Modbus request sent by the SlimLine, following some indications how to fix the problem.

Have you checked the serial mode set (The SlimLine default is 115200, e, 8), is it according to the Toshiba inverter requirements ?
Check serial connection, sometimes the D+/D- signals are misinterpreted, tries to reverse the connection.
The Modbus node sent by your program is 02, are you sure that the inverter has this modbus node ?
The register address is 0xFD01 (64769 decimal) it seems too high.
According to Modbus specifications the address sent is (Address-1) sometimes you have to add 1 to Address.
Activates the SpyOn, spying by a Telnet connection it can be seen how the FB is working (It’s a great help to troubleshooting).

[Anonimo]

I’ve changed the baud rate settings by the web page and have spied the FB working, here the reports of these actions (Screenshot).

As you can see in the spy report (Toolly screenshot) it seems that the Toshiba Inverter doesn’t answer to Modbus request. Have you any suggestion ?

[Sergio Bertana]

The fact that the inverter doesn’t answer excludes a wrong register address problem. If the address is wrong usually the device answers with a modbus error data frame. So the suggestions are to focusing on serial mode, Modbus node and cable wiring.

It’s a little bit strange the reception of an 00 code, have you correctly terminated with a 120 ohm resistor on both sides, the RS485 line ?

[Sergio Bertana]

We’ve managed to make the communication between the two devices; actually we were connecting the plc to the wrong port of the inverter (4-wire RS485 instead of 2-wire RS485) and after a second look we realised that, corrected it and bingo… everything is working perfectly. So to help other people here are the major lines to check:

The Baud rate, we reconfigured the baudrate of the PLC so it would be in the same range of the inverter.
Configure the inverter parameters to use the modbus protocol and setting the baud rate, the node (Refer to manual page 40-41).
For the connection we used a 2-wire RS485 cable, and we should short RXB to TXB and RXA to TXA on the inverter.
The modbus addresses of the inverter were correct (FD01, FC91…) (Refer to manual page 41, abstract).
We should add an offset of +1 to the Address in the FB ModbusMaster.

Thank’s a lot Bertaser for your assistance, and the solutions you gave us to find the problem.

[Autore]

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