How to set unit_id for ModbusTCPClient

[maba2402]

Hi,
I wanted to query a holding register for a ModbusTCPServer having a device ID of 2.
Here is the code:

from pymodbus.client import ModbusTcpClient

client = ModbusTcpClient(host='192.168.178.149',
                         port=502,
                         unit_id=2,
                         debug=True)
client.connect()

response = client.read_holding_registers(40001,5)
print(response)
client.close()

This results in the following print out:
Exception Response(131, 3, IllegalAddress)

Using wireshark gives the following details:

Here I see Unit Identifier = 0. I was expecting 2.
Any ideas?

[janiversen]

yes read the documentation, you are not using the proper calls.

[maba2402]

Hi,
I found the issue. It was a problem with so called alias adresses for the holding registers.
Subtracting 40001 from the register adresse solved the problem.
Sorry for bothering you.

Setting the device identifier was not the issue. This works BTW with

rr = client.read_holding_registers(1633, 1, slave=2)

BR
Marc