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ljean / modbus-tk

Create Modbus app easily with Python
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Exception writing multiple registers #137

Closed aetasoul closed 3 years ago

aetasoul commented 3 years ago

Hi, I'm trying to write string to the registers but I got the following exception with the code shown:

master.execute(slaveID, cst.WRITE_MULTIPLE_REGISTERS, registers[4] - 1, output_value=b'0000', data_format='ssss')

Traceback (most recent call last):
  File "scrivi.py", line 26, in <module>
    logger.info(master.execute(slaveID, cst.WRITE_MULTIPLE_REGISTERS, registers[4] - 1, output_value=b'0000', data_format='ssss'))
  File "/usr/local/opt/python-3.8.6/lib/python3.8/site-packages/modbus_tk/utils.py", line 39, in new
    raise excpt
  File "/usr/local/opt/python-3.8.6/lib/python3.8/site-packages/modbus_tk/utils.py", line 37, in new
    ret = fcn(*args, **kwargs)
  File "/usr/local/opt/python-3.8.6/lib/python3.8/site-packages/modbus_tk/modbus.py", line 225, in execute
    pdu += struct.pack(data_format, *output_value)
struct.error: argument for 's' must be a bytes object

The code is running with python3.8, before the upgrade with python2.7 it work

ljean commented 3 years ago

You may try to set the output value as a list : output_value = [b'0', b'0', b'0', b'0'] I hope it helps

aetasoul commented 3 years ago

Hi, sorry for the very late reply.

I can confirm that change from master.execute(slaveID, cst.WRITE_MULTIPLE_REGISTERS, registers[4] - 1, output_value=b'0000', data_format='ssss') to master.execute(slaveID, cst.WRITE_MULTIPLE_REGISTERS, registers[4] - 1, output_value=[b'0', b'0', b'0', b'0'], data_format='ssss') works.