[Modbus TCP] _readMemory error! Error: Data length error, expected 9 got 6

[Ralience123]

Hi！
I found a following error when using modbus tcp. Before testing fuxa,We checked the data type,tcp address and the slave address.They are correct,then I use modbus poll to read, there is no problem.

But when I use fuxa to read, the following error occurs. I tried to set up polling 5 sec,but it didn‘t work.

Your support is appreciated.

[rvbatista]

Do you know why Modbus pool is showing -- for two registers? Are you able to use Wireshark with both?

[Ralience123]

Yes,I use Wireshark to check the message both of them,and it didn't show any alarms or errors.

Do you know why Modbus pool is showing -- for two registers? Are you able to use Wireshark with both?

[rvbatista]

The device is answering with different lengths for the same request?
Could you also get the Wireshark requests for those answers?

[Ralience123]

I found something new today：There are no details about ‘Register’ under ‘Modbus’. Normally it should show up,like pic 2. Perhaps these messages were not recognized?
pic 1

pic 2

The device is answering with different lengths for the same request? Could you also get the Wireshark requests for those answers?

[IonuDragomir1]

Hi,
I get the same error for Modbus RTU. Did you find any solution to this?
My error message: 2024-04-12T11:16:53.352Z [ERR] 'ModbusRTU' _readMemory error! Error: Data length error, expected 11 got 1
After restarting the server, I get the values, but beside the above error, I also get this error: 2024-04-12T11:19:09.757Z [ERR] 'ModbusRTU' _readMemory error! Error: CRC error

[Ralience123]

Hi, I get the same error for Modbus RTU. Did you find any solution to this? My error message: 2024-04-12T11:16:53.352Z [ERR] 'ModbusRTU' _readMemory error! Error: Data length error, expected 11 got 1 After restarting the server, I get the values, but beside the above error, I also get this error: 2024-04-12T11:19:09.757Z [ERR] 'ModbusRTU' _readMemory error! Error: CRC error

Hi，
You can use some modbus software like Modbus Poll or QModMaster to check the message. I think maybe your device did not parsing the message correctly，you also can find the error code in the message.

[Github-User-002]

Hi I get the same CRC error on my polling, it only happens on ID: 5, holding register 2024 and duplpicate id: 1, 2001 and id: 5, HR: 2001, but only ID: 5 is showing the _readmemory error

Those messages look fine on modbus poll and wireshark, so I can't think the slave is doing anything wrong, it must be a bug in the FUXA

EDIT: If I make another device in Fuxa, with the register alone in it, then it shows up without problem. But I cannot have 2 devices on the same serial so it does not work as a workaround....

[unocelli]

Hi, have you try to update the modbus library to v8.0.16

[Ralience123]

Hi, have you try to update the modbus library to v8.0.16

Hi, I haven't upgraded this library yet, but I will do it later :）

[Ralience123]

Hi, have you try to update the modbus library to v8.0.16

Hi. after checking the tcp server, I found that there was a byte error in the reply message, which caused the number of bytes to be incorrect. Now I have updated the server version and the problem has been resolved, thanks for your help and you can close the issue :)

[maufc]

Hi.
I have this problem using ModbusTCP and Telnet, as a way to use ModbusRTUoverTCP.
I am not completely sure if RTUoverTCP is supported or not.
I find that 'trick' here:
#780
Anyway, I am getting _readMemory errors
Thanks!