minimalmodbus: Checksum error in rtu mode

Hi,

I’ve got an error when I try to select some bits or registers from a modbus slave.

#!/usr/bin/env python3

import serial
import minimalmodbus
from time import sleep

client1 = minimalmodbus.Instrument('/dev/ttyAMA0', 10, debug=True)  # port name, slave address (in decimal)
client1.serial.baudrate = 19200
client1.serial.bytesize = 8
client1.serial.parity   = serial.PARITY_EVEN
client1.serial.stopbits = 1
client1.serial.timeout  = 0.1
client1.mode = minimalmodbus.MODE_RTU

res = client1.read_register(1001, 1, 4)
print (res)

The Response

MinimalModbus debug mode. Create serial port /dev/ttyAMA0
MinimalModbus debug mode. Will write to instrument (expecting 7 bytes back): 0A 04 03 E9 00 01 E1 01 (8 bytes)
MinimalModbus debug mode. Clearing serial buffers for port /dev/ttyAMA0
MinimalModbus debug mode. No sleep required before write. Time since previous read: 1755610178.72 ms, minimum silent period: 2.01 ms.
MinimalModbus debug mode. Response from instrument: FB F8 7F 00 (4 bytes), roundtrip time: 0.1 ms. Timeout for reading: 100.0 ms.

Traceback (most recent call last):
  File "minimal.py", line 42, in <module>
    res = client1.read_register(1001, 1, 4)
  File "/usr/local/lib/python3.7/dist-packages/minimalmodbus.py", line 486, in read_register
    payloadformat=_Payloadformat.REGISTER,
  File "/usr/local/lib/python3.7/dist-packages/minimalmodbus.py", line 1245, in _generic_command
    payload_from_slave = self._perform_command(functioncode, payload_to_slave)
  File "/usr/local/lib/python3.7/dist-packages/minimalmodbus.py", line 1330, in _perform_command
    response, self.address, self.mode, functioncode
  File "/usr/local/lib/python3.7/dist-packages/minimalmodbus.py", line 1867, in _extract_payload
    raise InvalidResponseError(text)
minimalmodbus.InvalidResponseError: Checksum error in rtu mode: '\x7f\x00' instead of 'C\x02' . The response is: 'ûø\x7f\x00' (plain response: 'ûø\x7f\x00')

Do you have any recomendations for analyzing the problem?