pymodbus on Raspberry Pi 3B and Energy Meter Connection Error

Question

I've been having connection errors on my raspberry pi 3B using pymodbus. Designed a board using MAX14854G as the RS-485 transceiver that is connected to the RPI3's UART pins (8 & 10). It's connected to the m-system energy meter (53U-1211-AD4/H) through the T1, T2 & T4 (GND) pins.

Additional info: I'm using the full functionality of the UART by using this procedure: link

Here's my code:

In [3]: import pymodbus

In [4]: import serial.rs485

In [5]: from pymodbus.client.sync import ModbusSerialClient as ModbusClient

In [6]: from pymodbus.register_read_message import ReadInputRegistersResponse

In [7]: msys = ModbusClient(method='rtu',port='/dev/ttyAMA0',stopbits=1,bytesize=8,parity='N',baudrate=9600,timeout=5)

In [8]: msys.connect()
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-8-31c23cb3ed21> in <module>()
----> 1 msys.connect()

/usr/local/lib/python3.5/dist-packages/pymodbus/client/sync.py in connect(self)
474             self.close()
475         if self.method == "rtu":
--> 476             self.socket.interCharTimeout = self.inter_char_timeout
477             self.last_frame_end = None
478         return self.socket is not None

Update:

Followed @BenyaminJafari 's advice and changed the root permission:

sudo chmod 777 /dev/ttyAMA0

I can finally connect as per below code but resulted in a different error:

In [39]: msys.connect()
Out[39]: True

In [40]: valueHoldingRegisters = msys.read_holding_registers(1,1,unit=1)

In [41]: valueHoldingRegisters = msys.read_holding_registers(1,1,unit=1)

In [42]: valueHoldingRegisters.isError()
Out[42]: True

In [43]: print(valueHoldingRegisters)
Modbus Error: [Input/Output] Modbus Error: [Invalid Message] Incomplete message received, expected at least 2 bytes (0 received)

Error log:

DEBUG:pymodbus.transaction:Current transaction state - IDLE
DEBUG:pymodbus.transaction:Running transaction 1
DEBUG:pymodbus.transaction:SEND: 0x1 0x3 0x0 0x1 0x0 0x1 0xd5 0xca
DEBUG:pymodbus.client.sync:New Transaction state 'SENDING'
DEBUG:pymodbus.transaction:Changing transaction state from 'SENDING' to 'WAITING FOR REPLY'
DEBUG:pymodbus.transaction:Transaction failed. (Modbus Error: [Invalid Message] Incomplete message received, expected at least 2 bytes (0 received)) 
DEBUG:pymodbus.framer.rtu_framer:Frame - [b''] not ready
DEBUG:pymodbus.transaction:Changing transaction state from 'PROCESSING REPLY' to 'TRANSACTION_COMPLETE'
Unhandled error

Update (Added some new lines):

In [1]: import pymodbus

In [2]: import serial

In [3]: from pymodbus.pdu import ModbusRequest

In [4]: from pymodbus.client.sync import ModbusSerialClient as ModbusClient

In [5]: from pymodbus.transaction import ModbusRtuFramer

In [6]: from pymodbus.register_read_message import ReadInputRegistersResponse

In [7]: import logging

In [8]: logging.basicConfig()

In [9]: log = logging.getLogger()

In [10]: log.setLevel(logging.DEBUG)

In [11]: msys = ModbusClient(method='rtu',port='/dev/ttyAMA0',stopbits=1,bytesize=8,parity='N',baudrate=9600,timeout=2)

In [12]: connection = msys.connect()

In [13]: print(connection)
True

In [14]: HR1 = msys.read_holding_registers(0,1,unit=1)
DEBUG:pymodbus.transaction:Current transaction state - IDLE
DEBUG:pymodbus.transaction:Running transaction 1
DEBUG:pymodbus.transaction:SEND: 0x1 0x3 0x0 0x0 0x0 0x1 0x84 0xa
DEBUG:pymodbus.client.sync:New Transaction state 'SENDING'
DEBUG:pymodbus.transaction:Changing transaction state from 'SENDING' to 'WAITING FOR REPLY'
DEBUG:pymodbus.transaction:Transaction failed. (Modbus Error: [Invalid Message] Incomplete message received, expected at least 2 bytes (0 received)) 
DEBUG:pymodbus.framer.rtu_framer:Frame - [b''] not ready
DEBUG:pymodbus.transaction:Changing transaction state from 'PROCESSING REPLY' to 'TRANSACTION_COMPLETE'

In [15]: print(HR1)
Modbus Error: [Input/Output] Modbus Error: [Invalid Message] Incomplete message received, expected at least 2 bytes (0 received)

In [25]: HR2= msys.read_holding_registers(1,1,unit=1)
DEBUG:pymodbus.transaction:Current transaction state - TRANSACTION_COMPLETE
DEBUG:pymodbus.transaction:Running transaction 2
DEBUG:pymodbus.transaction:SEND: 0x1 0x3 0x0 0x1 0x0 0x1 0xd5 0xca
DEBUG:pymodbus.framer.rtu_framer:Changing state to IDLE - Last Frame End - None, Current Time stamp - 1478195437.918486
DEBUG:pymodbus.client.sync:New Transaction state 'SENDING'
DEBUG:pymodbus.transaction:Changing transaction state from 'SENDING' to 'WAITING FOR REPLY'
DEBUG:pymodbus.transaction:Incomplete message received, Expected 7 bytes Recieved 0 bytes !!!!
DEBUG:pymodbus.transaction:Changing transaction state from 'WAITING FOR REPLY' to 'PROCESSING REPLY'
DEBUG:pymodbus.transaction:RECV: 
DEBUG:pymodbus.framer.rtu_framer:Frame - [b''] not ready
DEBUG:pymodbus.transaction:Changing transaction state from 'PROCESSING REPLY' to 'TRANSACTION_COMPLETE'

In [26]: print(HR2)
Modbus Error: [Input/Output] No Response received from the remote unit/Unable to decode response

In [27]: HR3 = msys.read_holding_registers(2,1,unit=1)
DEBUG:pymodbus.transaction:Current transaction state - TRANSACTION_COMPLETE
DEBUG:pymodbus.transaction:Running transaction 3
DEBUG:pymodbus.transaction:SEND: 0x1 0x3 0x0 0x2 0x0 0x1 0x25 0xca
DEBUG:pymodbus.framer.rtu_framer:Changing state to IDLE - Last Frame End - 1478195439.927521, Current Time stamp - 1478195492.844382
DEBUG:pymodbus.client.sync:New Transaction state 'SENDING'
DEBUG:pymodbus.transaction:Changing transaction state from 'SENDING' to 'WAITING FOR REPLY'
DEBUG:pymodbus.transaction:Incomplete message received, Expected 7 bytes Recieved 0 bytes !!!!
DEBUG:pymodbus.transaction:Changing transaction state from 'WAITING FOR REPLY' to 'PROCESSING REPLY'
DEBUG:pymodbus.transaction:RECV: 
DEBUG:pymodbus.framer.rtu_framer:Frame - [b''] not ready
DEBUG:pymodbus.transaction:Changing transaction state from 'PROCESSING REPLY' to 'TRANSACTION_COMPLETE'

In [28]: print(HR3)
Modbus Error: [Input/Output] No Response received from the remote unit/Unable to decode response

Can someone please help and suggest where I'm going wrong ?

Is your problem in .connect()? Is your connection value equal to False? Is this error consider to client.connect()?! Please put on your full trace of the error for better sense. — Benyamin Jafari
Did you set the root permsion on /dev/ttyAMA0 with sudo chmod 777 /dev/ttyAMA0? — Benyamin Jafari
Please show the COMPLETE stacktrace, not a part that also has been edited by you - NoneTyoe for sure is not what the error read. — deets
@BenyaminJafari I can't connect to my energy meter at all using .connect(). Not even False but interCharTimeout. Updated original post for the full code and errors. Thank you! — cknz
@deets Updated original post for the full code and errors. Thank you! — cknz

Benyamin Jafari Benyamin Jafari · Accepted Answer · 2018-12-06T09:44:13

I set the Modbus slave logging for getting more information:

import logging
from pymodbus.client.sync import ModbusSerialClient as ModbusClient

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

msys = ModbusClient(
    method='rtu', port='/dev/ttyAMA0',
    stopbits=1, bytesize=8, parity='N',
    baudrate=9600, timeout=5
)

if msys.connect():
    try:
        valueHoldingRegisters = msys.read_holding_registers(1, 1, unit=1)

        if not valueHoldingRegisters.isError():
            print(valueHoldingRegisters.registers)

        else:
            raise ValueError(valueHoldingRegisters)

    except Exception as exc:
        print(exc)

else:
    print('Connection error')

msys.close()

[NOTE]:

Make sure your port should be has a root permission using:

sudo chmod 777 /dev/ttyAMA0

pymodbus on Raspberry Pi 3B and Energy Meter Connection Error

1 Answers