[Minimalmodbus-list] Cannot communicate through USB-RS485 using minimalmodbus

[Michelle N. <to...@gm...>]

To whom may concern,

Thank you for your attention on my issue.

I tried to use minimalmodbus to communicate modbus device through USB-RS485
cable.
Device number is 66, baud rate = 192000, Parity = Even, Stop bit = 1,
bytesize = 8

My code is:

import minimalmodbus
import serial
instrument = minimalmodbus.Instrument('COM12', 66)

instrument.serial.parity = serial.PARITY_EVEN

print(instrument)

> minimalmodbus.Instrument<id=0x4f0b780, address=66, mode=rtu,
> close_port_after_each_call=False, precalculate_read_size=True, debug=False,
> serial=Serial<id=0x51860b8, open=True>(port='COM12', baudrate=19200,
> bytesize=8, parity='E', stopbits=1, timeout=0.05, xonxoff=False,
> rtscts=False, dsrdtr=False)>


My device modebus objects like:
[image: Inline image 1]

When I tried to read the vale of Room Humidity Display, I used:
instrument.read_register(10, 0)
It replied:

> ---------------------------------------------------------------------------
> OSError                                   Traceback (most recent call last)
> <ipython-input-6-ae322845b016> in <module>()
> ----> 1 instrument.read_register(10, 0)
> C:\ProgramData\Anaconda3\lib\site-packages\minimalmodbus-0.7-py3.6.egg\minimalmodbus.py
> in read_register(self, registeraddress, numberOfDecimals, functioncode,
> signed)
>     256         _checkInt(numberOfDecimals, minvalue=0, maxvalue=10,
> description='number of decimals')
>     257         _checkBool(signed, description='signed')
> --> 258         return self._genericCommand(functioncode, registeraddress,
> numberOfDecimals=numberOfDecimals, signed=signed)
>     259
>     260
> C:\ProgramData\Anaconda3\lib\site-packages\minimalmodbus-0.7-py3.6.egg\minimalmodbus.py
> in _genericCommand(self, functioncode, registeraddress, value,
> numberOfDecimals, numberOfRegisters, signed, payloadformat)
>     695
>     696         ## Communicate ##
> --> 697         payloadFromSlave = self._performCommand(functioncode,
> payloadToSlave)
>     698
>     699         ## Check the contents in the response payload ##
> C:\ProgramData\Anaconda3\lib\site-packages\minimalmodbus-0.7-py3.6.egg\minimalmodbus.py
> in _performCommand(self, functioncode, payloadToSlave)
>     793
>     794         # Communicate
> --> 795         response = self._communicate(request,
> number_of_bytes_to_read)
>     796
>     797         # Extract payload
> C:\ProgramData\Anaconda3\lib\site-packages\minimalmodbus-0.7-py3.6.egg\minimalmodbus.py
> in _communicate(self, request, number_of_bytes_to_read)
>     928
>     929         if len(answer) == 0:
> --> 930             raise IOError('No communication with the instrument
> (no answer)')
>     931
>     932         return answer
> OSError: No communication with the instrument (no answer)


I also tried:
* instrument.read_register(10, 0, 3)
* instrument.read_register(10, 1, 3)
* instrument.read_register(40010, 1, 3)

All the above commands had the same error message.

How could I communicate with modbus device using minimalmodbus.

Thank you so much!

Best regards,

Michelle