Drive SD328A does not respond to Modbus RTU communication

[FlorinG]

Hello,

I am using a drive SD3 28A that is configured after first time use to work with Modbus RTU. The drive is in status READY. There is no motor connected yet, or other signals, but STO inputs.

I connected the Lexium CT program to the drive and everything goes well. I can read and write parameters. From time to time I got the error Nodeguard B201. MBnode_guard parameter (Mb 5644) is strangely 5000ms, instead of factory settings, 0. Even after restoring factory settings, it stays at 5000ms.

Using Modbus Poll or PLC M221 to read and write on the drive SD3 28A does not work, while the communication is established.

Using Modbus Slave emulator to check the PLC communication, it works, both ways, Readvar/Writevar or IO scan. PLC looks fine.

In relation with Modbus Poll, Modbus Slave and Lexium CT am using a converter from USB to RS485.

Between the PLC and the drive I am using a 2m long Ethernet shielded cable.

Why Lexium CT works with the drive and Modbus Poll and PLC does not work?

I also observed that the write function 06 is returned with illegal function, while write function 16 is legal, but is returned with illegal data error. Both functions are specified in the drive manual.

Concrete example 1:

I attached an extract of relevant communication instances between Lexium CT, Modbus Poll and the drive SD3 28A. We observed the error returned by Modbus Poll.

Concrete example 2:

With the PLC I use IO scanner for reading the registers:
6916
6918
5644
IOScanner is operational %SW210=2
(additional test of functioning: if I remove the cable from the socket RJ45, the status word %SW210 becomes 3)
The drive does not communicate on channel 1 %IWNS100=0.
I reset the communicaton with %S110=1 and it does not move.
SL1 LED from the PLC M221 blinks correctly, at 1/s, the scanning rate.

Other comments:

I didn't use a different Modbus master emulator. I didn't adapt the cable with end resistors.