ReadDeviceInformationRequest returns None

[Adam L]

Hi everybody!

It's my first post in the google group so...nice to meet you guys :) I'm quite new with modbus and recently I decided to implement some simple functionality to my app. I tested examples and synchronous-client.py combined with synchronous-server.py work as I expected. Today I was trying to test examples from synchronous-client-ext.py and my script stuck at command ReadDeviceInformationRequest(), which returns None after execution. I'm using pymodbus 1.2.0 (installed by pip) and python 3.4. Here is some code cutted to minimum.

test_server.py

#!/usr/bin/env python
from pymodbus.server.sync import StartTcpServer
from pymodbus.device import ModbusDeviceIdentification
import logging

logging.basicConfig()
log = logging.getLogger()
log.setLevel(logging.DEBUG)

identity = ModbusDeviceIdentification()
identity.VendorName  = 'Pymodbus'
identity.ProductCode = 'PM'
identity.VendorUrl   = 'http://github.com/bashwork/pymodbus/'
identity.ProductName = 'Pymodbus Server'
identity.ModelName   = 'Pymodbus Server'
identity.MajorMinorRevision = '1.0'

StartTcpServer(identity=identity, address=("localhost", 502))

test_client.py

#!/usr/bin/env python

from pymodbus.client.sync import ModbusTcpClient as ModbusClient
from pymodbus.mei_message import *
import logging

logging.basicConfig()
log = logging.getLogger()
log.setLevel(logging.DEBUG)

client = ModbusClient('127.0.0.1')
client.connect()

rq = ReadDeviceInformationRequest()
rr = client.execute(rq)
print(rr) #gives None

client.close()

server's console output:

DEBUG:pymodbus.server.sync:Started thread to serve client at ('127.0.0.1', 61107)
DEBUG:pymodbus.server.sync:Client Connected [127.0.0.1:61107]
DEBUG:pymodbus.server.sync:0x0 0x1 0x0 0x0 0x0 0x5 0x0 0x2b 0xe 0x1 0x0
DEBUG:pymodbus.transaction:0x0 0x1 0x0 0x0 0x0 0x5 0x0 0x2b 0xe 0x1 0x0
DEBUG:pymodbus.factory:Factory Request[43]
DEBUG:pymodbus.server.sync:Client Disconnected [127.0.0.1:61107]

and client's output:

DEBUG:pymodbus.transaction:Running transaction 1
DEBUG:pymodbus.transaction:
DEBUG:pymodbus.transaction:getting transaction 1
None

could you tell me how I could perform correct ReadDeviceInformationRequest? I tested Serial version with simple hardware loop between two devices, but failed with the same result...

[Adam L]

After checking on another machine the newest pymodbus version for python 2.x ("Bumping the version to 1.3.0 ", commit eb51b4df4f) everything works fine. Does anybody have info about this issue/bug? Unfortunately I have to use python 3.x in my project...

greets,
Adam

[Galen Collins]

There is a python 3 branch on github, see if that works for you.

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[Adam L]

Hi Bashwork,

I've tried with cloned branch for python3 (commit from 2013-07-21) but with the same result...also test_mei_messages.py gives me error:

F......
======================================================================
FAIL: testReadDeviceInformationRequest (__main__.ModbusMeiMessageTest)
Test basic bit message encoding/decoding
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Users\alutkows\git\pymodbus\test\test_mei_messages.py", line 55, in testReadDeviceInformationRequest
    self.assertTrue(result.information[0x02], "v2.1.12")
AssertionError: '' is not true : v2.1.12

----------------------------------------------------------------------
Ran 7 tests in 0.002s

I've tried with connection over TCP, Serial(ascii, rtu, binary) with the same result... should I somehow download version for python 2.x and convert it? Do you have any possibility to test it on python 3.4?

[Adam L]

Finally I think I found  a bug. In master and python3 branch is a wrong _rtu_frame_size for MEI message ReadDeviceInformationRequest.

mei-messages.py

class ReadDeviceInformationRequest(ModbusRequest):
    (...)

    function_code = 0x2b
    sub_function_code = 0x0e
    _rtu_frame_size = 3

If we use RTU framer, it will get this wrong value directly from the class instead of calculating it. For this request correct size should be 7.

1b - [UID]
1b - [0x2b]
1b - [0x0e]
1b - [Read Device ID code]
1b - [Object ID]
2b - [CRC]

After changes everything works fine.