Trouble getting data using Modbus/TCP with RTU

[Vivek Dwivedi]

Greetings:

I have an external device (Mass Flow Controller) with an ethernet port that can be interfaced using Modbus/TCP with RTU:

An example register map for this device is:

I/O description:  Flow

Modbus Function Code (read): 4

Reference Register Number: 0x4000

Number of Registers: 2

Unit: sccm

Data Type: float 4 byte

I am connecting to this device as follows using the ModbutRTUFramer...

from pymodbus.constants import Endian

from pymodbus.payload import BinaryPayloadDecoder

from pymodbus.payload import BinaryPayloadBuilder

from pymodbus.client.sync import ModbusTcpClient as ModbusClient

from pymodbus.transaction import ModbusRtuFramer

import logging

logging.basicConfig()

log = logging.getLogger()

log.setLevel(logging.INFO)

client = ModbusClient('192.168.2.176',port=502,framer=ModbusRtuFramer)

client.connect()

address = 0x4000

count = 2

result  = client.read_input_registers(address, count)

My print results always give me "None"

What am I doing wrong???

Any help will be appreciated

[Galen Collins]

Can you let me know what version you are using?  There was a regression with this use case that was fixed in the most recent release on github.  Could you make sure that you are using that code.  Also, here is a complete working example (which looks like what you are already using):

https://pymodbus.readthedocs.org/en/latest/examples/changing-framers.html

Could you also add any logging information that may be output?

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[Vivek Dwivedi]

Greeting thank you for prompt reply.  I have tried to reinstall pymodbus using the example given by:

git clone git://github.com/bashwork/pymodbus.git

cd pymodbus

sudo python setup.py install

however, using this method I get the following errors:

Best match: Twisted 13.0.0

Downloading https://pypi.python.org/packages/source/T/Twisted/Twisted-13.0.0.tar.bz2#md5=68afff4e1efd3757d934e39f70c99f57

Processing Twisted-13.0.0.tar.bz2

Writing /tmp/easy_install-gtv0K3/Twisted-13.0.0/setup.cfg

Running Twisted-13.0.0/setup.py -q bdist_egg --dist-dir /tmp/easy_install-gtv0K3/Twisted-13.0.0/egg-dist-tmp-mdZ9io

cc1: error: unrecognized command line option "-arch"

cc1: error: unrecognized command line option "-arch"

cc1: error: unrecognized command line option "-arch"

cc1: error: unrecognized command line option "-arch"

cc1: error: unrecognized command line option "-arch"

cc1: error: unrecognized command line option "-arch"

error: Setup script exited with error: command 'gcc' failed with exit status 1

I am on an OS X machine.

Thank you again.

[Vivek Dwivedi]

I reran the code and I still get "none"

>>> from pymodbus.constants import Endian

>>> from pymodbus.payload import BinaryPayloadDecoder

>>> from pymodbus.payload import BinaryPayloadBuilder

>>> from pymodbus.client.sync import ModbusTcpClient as ModbusClient

>>> from pymodbus.transaction import ModbusRtuFramer

>>> import logging

>>> logging.basicConfig()

>>> log = logging.getLogger()

>>> log.setLevel(logging.INFO)

>>> client = ModbusClient('192.168.2.176',port=502,framer=ModbusRtuFramer)

>>> client.connect()

True

>>> address = 0x4000

>>> count   = 2

>>> result  = client.read_input_registers(address, count)

>>> print result

None

>>> result  = client.read_input_registers(address, 29)

>>> print result

None

>>> address = 0x4002

>>> print result  = client.read_input_registers(address, count)

SyntaxError: invalid syntax

>>> result  = client.read_input_registers(address, count)

>>> print result

None

On Thursday, May 9, 2013 12:08:04 AM UTC-4, Bashwork wrote:

[Galen Collins]

Oh, I actually haven't tested installing twisted on osx too much.  What you can do for the short term is simply remove or comment the twisted dependency out in the setup.py as you are not using it anyways.

Galen

[Galen Collins]

Have you set the logging to DEBUG and seen if there is anything printed out?

[Vivek Dwivedi]

Ok, I downloaded the pymodbus-master from the git and removed any mention of "Twisted" and reinstalled.

[Vivek Dwivedi]

Here is my debug results:

DEBUG:pymodbus.transaction:Running transaction 1

DEBUG:pymodbus.transaction:Transaction failed. (timed out) 

DEBUG:pymodbus.transaction:Transaction failed. (timed out) 

DEBUG:pymodbus.transaction:Transaction failed. (timed out) 

DEBUG:pymodbus.transaction:getting transaction 1

Traceback (most recent call last):

  File "/Users/vivekd/Desktop/test.py", line 60, in <module>

    decoder = BinaryPayloadDecoder.fromRegisters(result.registers, endian=Endian.Little)

AttributeError: 'NoneType' object has no attribute 'registers'

[Galen Collins]

So it looks like your device isn't responding to the requests.  Can you give me more information about your device so I can look at a data sheet or can you use another utility (say http://www.modbusdriver.com/modpoll.html) to quickly see if you can get any kind of response at all?

Galen

[Vivek Dwivedi]

Thank you Galen:

Are you aware of a utility that I can use under OS X?  BTW if I want to remove the pymodbus library and reinstall it, what would be the best way to go about it?

Thanks.

--Vivek

[Galen Collins]

I actually do all my development under Linux, so I don't really know any quick utilities. I know there is the jamod java library, but I don't think it has any utilities built for it.

As for uninstalling, I would recommend running in virtualenv with pip as the easiest way to manage dependencies. Then it is just pip uninstall pymodbus.

With easy install, you actually need to manually delete the .egg file or directory (more information can be found by googling easy_install).

Galen

[Vivek Dwivedi]

Ok, so I am using ModBus Probe, http://www.modbusapps.com/mbp.php to see if I can connect to my device and read input registers and I can.

in python 2.7 however I still get the following error:

>>> import pymodbus

>>> from pymodbus.client.sync import ModbusTcpClient as ModbusClient

>>> from pymodbus.transaction import ModbusRtuFramer

>>> import logging

>>> logging.basicConfig()

>>> log = logging.getLogger()

>>> log.setLevel(logging.DEBUG)

>>> client = ModbusClient('192.168.2.176',port=502,framer=ModbusRtuFramer)

>>> client.connect()

True

>>> address = 0x4000

>>> count   = 2

>>> result  = client.read_input_registers(address, count)

DEBUG:pymodbus.transaction:Running transaction 1

DEBUG:pymodbus.transaction:Transaction failed. (timed out) 

DEBUG:pymodbus.transaction:Transaction failed. (timed out) 

DEBUG:pymodbus.transaction:Transaction failed. (timed out) 

DEBUG:pymodbus.transaction:getting transaction 1

[Vivek Dwivedi]

Galen:

I want to make sure that I am installing pymodbus without the twisted dependencies properly, this is what I do:

git clone git://github.com/bashwork/pymodbus.git

cd pymodbus 

I edit the setup.py file and comment out:

install_requires = [

       # 'twisted >= 12.2.0',

        'pyserial >= 2.6'

    ],

I then cd..

and run

vhdapple:Desktop vivekd$ easy_install pymodbus 

and here is my output:

vhdapple:Desktop vivekd$ easy_install pymodbus

Processing pymodbus

Writing /Users/vivekd/Desktop/pymodbus/setup.cfg

Running setup.py -q bdist_egg --dist-dir /Users/vivekd/Desktop/pymodbus/egg-dist-tmp-nwdZ2g

Adding pymodbus 1.2.0 to easy-install.pth file

Installed /Library/Frameworks/Python.framework/Versions/7.3/lib/python2.7/site-packages/pymodbus-1.2.0-py2.7.egg

Processing dependencies for pymodbus==1.2.0

Finished processing dependencies for pymodbus==1.2.0

Does this look correct??

Thanks.

On Thursday, May 9, 2013 5:45:31 PM UTC-4, Bashwork wrote:

[Galen Collins]

That is fine.

[Vivek Dwivedi]

Ok, so I know for a fact that I can read my device using Modbus probe...Here is code:

from pymodbus.constants import Endian

from pymodbus.payload import BinaryPayloadDecoder

from pymodbus.payload import BinaryPayloadBuilder

from pymodbus.client.sync import ModbusTcpClient as ModbusClient

from pymodbus.transaction import ModbusRtuFramer

#---------------------------------------------------------------------------# 

# configure the client logging

#---------------------------------------------------------------------------# 

import logging

logging.basicConfig()

log = logging.getLogger()

log.setLevel(logging.DEBUG)

#---------------------------------------------------------------------------# 

# We are going to use a simple client to send our requests

#---------------------------------------------------------------------------# 

client = ModbusClient('192.168.2.176',port=502,framer=ModbusRtuFramer)

client.connect()

address = 0x4000

count   = 2

result  = client.read_input_registers(address,count)

print result

#---------------------------------------------------------------------------# 

# close the client

#---------------------------------------------------------------------------# 

client.close()

and here is the result:

>>> 

DEBUG:pymodbus.transaction:Running transaction 1

DEBUG:pymodbus.transaction:Transaction failed. (timed out) 

DEBUG:pymodbus.transaction:Transaction failed. (timed out) 

DEBUG:pymodbus.transaction:Transaction failed. (timed out) 

DEBUG:pymodbus.transaction:getting transaction 1

None

I can't figure out what is wrong.  I'm attaching a short excerpt of the modbus codes....I'm at an impasse and I can't figure out what I am doing wrong.

[Vivek Dwivedi]

Ok, So I have been able to communicate (get and receive info) by not using the RTU framework though it states in my manual that my device is Modbus/TCP with RTU protocol.

On Friday, May 10, 2013 11:05:38 PM UTC-4, Bashwork wrote:

[Galen Collins]

Oh, is your device a modbus TCP that also supports RTU?  That makes more sense and you can test this by directly connecting to your device's serial port and using the serial client with RTU.  For now, I would recommend just using the TCP going forward if it works.

Galen

Sorry again for the slow responses, I have been pretty busy lately.