'ModbusIOException' object has no attribute 'registers'

[Howeng98]

Versions

• Python: 3.7
• OS: Linux
• Pymodbus: 1.3.1
• Pymodbus3: 1.0.0
• Modbus Hardware (if used):

Description

I want to use Modbus to execute JY-CZ1000-GN. And I use the code as below, and It can't worked. The point is it can worked last time (a few weeks ago),but now cannot.
I wonder that maybe it is not the software(code) problem, should be handware problem, I guess it is the wire didn't connect to ground ,so when we try to read register will received some circuit noise(?)

Code and Logs

Code:
from pymodbus.client.sync import ModbusSerialClient as ModbusClient

scale = ModbusClient(method='rtu', port='/dev/ttyUSB0', parity='N', baudrate=9600, bytesize=8, stopbits=2, timeout=1)
connection = scale.connect()

try:
result = scale.read_holding_registers(0,10, unit=1)
print(result)
print(result.registers)
except Exception as e:
print(e)

scale.close()

Error Message:
Modbus Error: [Input/Output] No Response received from the remote unit
'ModbusIOException' object has no attribute 'registers'

[dhoomakethu]

Try using the kwarg strict=False when initializing the client on windows environment.
scale = ModbusClient(method='rtu', port='/dev/ttyUSB0', parity='N', baudrate=9600, bytesize=8, stopbits=2, timeout=1, strict=False). Please share the logs if you are still having the issues.

[Howeng98]

@dhoomakethu
Hi sir, sorry for typo , I am using Linux for running this code
And I had tried to add 'strict' into that line, but the error message still same as before

Error Msg:
Modbus Error: [Input/Output] No Response received from the remote unit
'ModbusIOException' object has no attribute 'registers'

I also had tried:

1. use time.sleep(1) to make it delay for received complete data message
2. raise Timeout be higher
3. use pymodbus with 1.3.1 version
4. use pymodbus3
   but still got same error :(

[dhoomakethu]

Please use the latest version of pymodbus (2.2.0) and see if it solves the issue. The issue could also be due to wrong serial settings. Please share the logs for further analysis.

[Howeng98]

@dhoomakethu
Thanks for your suggestion sir, I have try to use pymodbus (2.2.0) version but it still can't work.

Log:
DEBUG:pymodbus.transaction:Current transaction state - IDLE
DEBUG:pymodbus.transaction:Running transaction 1
DEBUG:pymodbus.transaction:SEND: 0x10 0x4 0x0 0x0 0x0 0xa 0x73 0x4c
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:Getting transaction 16
DEBUG:pymodbus.transaction:Changing transaction state from 'PROCESSING REPLY' to 'TRANSACTION_COMPLETE'
odbus Error: [Input/Output] Modbus Error: [Invalid Message] Incomplete message received, expected at least 2 bytes (0 received)
'ModbusIOException' object has no attribute 'registers'

I will try another way to solve it

[tompropst]

I am seeing this same error. In my case, I'm connecting over TCP and most the register reads succeed. Only about once a day (or less) do I see this error while reading every 10 seconds.

From the log output above, it looks like the incomplete message should be raising an exception but perhaps it is being ignored someplace so the actual exception occurs when trying to access the registers of the return object.

[tracernz]

Those exceptions are caught and returned by functions higher up. As you can see in @Howeng98 reply above:

'ModbusIOException' object has no attribute 'registers'

The way error handling currently works in the public pymodbus API is exception objects are returned, not raised as exceptions. See the comment by @dhoomakethu #298 (comment), and that issue for wider context.

[DevHasher]

I m facing the same issue. Any solution was found?

[dhoomakethu]

use result.isError() to validate if the result is a valid response or an error response.

[DevHasher]

@dhoomakethu So to resolve the 'ModbusIOException' object has no attribute 'registers' i try resending the request multiple times till i receive a proper response.
Currently using a while loop.
Is there a service in pymodbus doing the same?

[dhoomakethu]

@AnkitaPadma I am afraid that's the way to go. In general, unless the communication is not stable the slaves should/would return the positive response. You can also check what kind of error is being returned to debug further.

[jsr1611]

Hi folks,

I do face a similar issue.

I receive data but sometimes, it gives me the same error. Here is my print:

Count ID Temp Humidity Part03 Part05 DateTime
...
5 4 23.28 49.51 6631 759 2020-07-14 11:22:19.464
6 1 24.4 46.74 9259 848 2020-07-14 11:22:20.231
6 3 24.32 47.02 7334 1492 2020-07-14 11:22:20.631
6 4 23.26 49.52 6641 760 2020-07-14 11:22:21.031
'ModbusIOException' object has no attribute 'registers'
8 1 24.38 46.7 9279 844 2020-07-14 11:22:26.627
8 2 24.73 45.81 8243 867 2020-07-14 11:22:26.627
8 3 24.3 46.97 7293 1474 2020-07-14 11:22:27.251
8 4 23.26 49.55 6699 763 2020-07-14 11:22:27.731
9 1 24.42 46.7 9287 842 2020-07-14 11:22:28.402
9 2 24.73 45.77 8252 868 2020-07-14 11:22:28.403
9 3 24.34 46.95 7293 1465 2020-07-14 11:22:29.026
9 4 23.25 49.52 6704 764 2020-07-14 11:22:29.282
10 1 24.43 46.73 9294 841 2020-07-14 11:22:30.161
'ModbusIOException' object has no attribute 'registers'
11 1 24.4 46.75 9329 838 2020-07-14 11:22:35.453
11 2 24.75 45.78 8276 870 2020-07-14 11:22:35.453
11 3 24.32 47.0 7362 1452 2020-07-14 11:22:35.853
11 4 23.25 49.55 6720 763 2020-07-14 11:22:36.413
...

I am using it like this:
sensor1 = [modbusClient.read_input_registers(address=10, count=6, unit=1)]
register address=10,
count = 6 (reading all data I need at once stored as an array)
slave address = 1,

And, as it gives me the above error message it is missing inbetween sensor data.

[copyCat304]

I found via trial and error that there should be atleast 20sec delay between register read or write call.

from pymodbus.client.sync import ModbusSerialClient as ModbusClient
from pymodbus.constants import Endian
from pymodbus.payload import BinaryPayloadDecoder
from pymodbus.payload import BinaryPayloadBuilder
import time
print("import ok")
client = ModbusClient(method='rtu', bytesize = 8, baudrate = 9600,port='COM8', timeout=3, strict=False)
while(True):
if client.connect():
print("connected*")
# connection is OK
# read floats
result = client.read_holding_registers(0, 4, unit=1)
print(result.registers)
decoder = BinaryPayloadDecoder.fromRegisters(result.registers, Endian.Big, wordorder=Endian.Little)
print("reslut01: " + str(decoder.decode_32bit_float()))
time.sleep(20)
result1 = client.read_holding_registers(20, 4, unit=1)
print(result1.registers)
decoder = BinaryPayloadDecoder.fromRegisters(result1.registers, Endian.Big, wordorder=Endian.Little)
print("reslut02: " + str(decoder.decode_32bit_float()))
time.sleep(20)
result2 = client.read_holding_registers(8, 2, unit=1)
print(result2.registers)
decoder = BinaryPayloadDecoder.fromRegisters(result2.registers, Endian.Big, wordorder=Endian.Little)
print("result03: " + str(decoder.decode_32bit_float()))
print("********************************")
time.sleep(20)
client.close()

I hope this helps and please let me know if there is any efficient way of doing this task I am kinda a newbie.

[obaidullahaamer]

Getting same issue. I tried Adding 20 sec delay and it worked. But is there any efficient way to solve this issue. That would make my life a lot easier.

[dhoomakethu]

@obaidullahaamer it all boils down to how fast the modbus slave is responding and how many registeres are being queried. Ideally the client should not have to wait for 20sec to get the values. What is the model and make of your slave?