Modbus TCP Transaction ID >255

[Kudie86]

Versions

• Python: 2.7
• OS:
• Pymodbus: 1.4

Pymodbus Specific

• Server: tcp - async
• Client: tcp - sync

Description

Hello,

I have a async modbus TCP server running on a RaspberryPi and a windows computer as a sync client. With pymodbus 1.4.0 the server stops responding after several time, which is not the case with pymodbus 1.3.2. I checked with wireshark and found out that the server does not respond to Transaction IDs larger than 255. When I start a new client, which starts with Transaction ID 1, the server is again running until Transaction ID 255.

Best regards,
Jörg

[dhoomakethu]

Could you please attach the debug logs for both client and server.

[Kudie86]

logging_client.log
logging_server.log

Attached the logs.
The client has a timeout at transaction 256 (row 1793). The position where the server stops is in row 2983 in the server log.
I use a single thread (threading library) to read data out of the data store in the server and put it to a digital-analog-converter.

[dhoomakethu]

Got it thanks, I could reproduce the b issue and found out the reason. Will give you a patch by tomorrow

[dhoomakethu]

@Kudie86 Please use this branch and see if it fixes your issue.
https://github.com/riptideio/pymodbus/tree/%23256-Fix-TCP-Server-Transactions

[Kudie86]

Great, it is working now! Thanks!