pymodbus does not read registers

Question

I am developing a program to read Modbus data via serial RTU using pymodbus.

My purpose is to read data from an ABB XRCG4 Xseries flow computing PC. I know that the COM port on the device side is COM1 and the serial protocol is RS232, on my PC, using a serial converter I am trying to connect to it. I know the configuration as follows:

PROTOCOL= 'rtu'

USB_PORT = 'COM4'

PARITY = 'None'

BAUD_RATE = 9600

TIMEOUT = 3

For test purposes I made an Arduino board into a Modbus Slave. I can read the data from the board with QModMaster, Modbus Pool and SimplyModbusMaster but I am unable to do so with my script. For the board I am unable to read anything at all, not eve with the programs mentioned above.

When I use the above mentioneds program to read data from the Arduino, everything works fine, when I try with my script, I get the AttributeError: 'ModbusIOException' object has no attribute 'registers'

I also noticed that I get this error if I unplug the cable while connection is running.

What am I missing? My guess is that I might not have a hardware dealer for the dsrdtr exchange, according to page 24 of the pymodbus documentation or maybe on the board side, the Register Format is not ok for my code.

Here you can see the details from the ABB board

Port description part1

Port description part2

My code:

from pymodbus.client.sync import ModbusSerialClient as ModbusClient
from pymodbus.client.sync import *
from pymodbus.register_read_message import *
from pymodbus.constants import Endian
from pymodbus.payload import BinaryPayloadDecoder
from pymodbus.payload import BinaryPayloadBuilder
from pymodbus.compat import iteritems
from pymodbus.exceptions import *
import time

import logging
import logging.handlers as Handlers

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

USB_PORT = 'COM4'
PARITY = 'N' #'N'
BAUD_RATE = 9600
TIMEOUT = 0.15


client = ModbusClient(method='rtu',
                  port=USB_PORT,
                  stopbits=1,
                  bytesize=8,
                  parity=PARITY,
                  baudrate=BAUD_RATE,
                  timeout=TIMEOUT, )



while True:

    connection = client.connect()
    #print(client.)
    print(f"COM Details {client.socket}")
    #client.socket.setRTS(True)
    print(f"Connection status is: {connection} \nClient State: {client.state} \nTimeout: {client.timeout}")
    #print(client.get_serial_settings)

    try:
        #################################### CITIM INPUT REGISTER (adresa,nr de registrii si unit ID
        input_value = client.read_input_registers(count=0x01,address=10,unit=0x01)
        #client.socket.setRTS(False)
        print(input_value)
    
        decoder = BinaryPayloadDecoder.fromRegisters(input_value.registers, byteorder=Endian.Little)
        decoded = {
            'string': decoder.decode_string(8),
            'float': decoder.decode_32bit_float(),
            '16uint': decoder.decode_16bit_uint(),
            'ignored': decoder.skip_bytes(2),
            #'8int': decoder.decode_8bit_int(),
            'bits': decoder.decode_bits(),}

        ############### CITIM HOLDING REGISTER  (exemplu, modelul vantilatorului)
        holding_values = client.read_holding_registers(0xD1A5,6,unit=0x01)


        holding_decoder = BinaryPayloadDecoder.fromRegisters(holding_values.registers, byteorder=Endian.Big)
        holding_decoded = {
            'string': holding_decoder.decode_string(8),
            #'float': holding_decoder.decode_32bit_float(),
            #'16uint': holding_decoder.decode_16bit_uint(),
            'ignored': holding_decoder.skip_bytes(2),
            #'8int': holding_decoder.decode_8bit_int(),
            'bits': holding_decoder.decode_bits(),
        }
        print("-" * 60)
        print("INPUT REGISTERS:")
        print("-" * 60)
        print(f"\nResponse: {input_value.registers} \nInput Registers Decoded values: \n")
        for name, value in iteritems(decoded):
            print ("%s\t" % name, value)
        print(f"\n Decoded speed: {decoded['float']}")
        print(f"Holding values registers:\n {holding_values.registers}")
        print("-" * 60)
        print("Holding Values Decoded Data")
        print("-" * 60)
        for name, value in iteritems(holding_decoded):
            print ("%s\t" % name, value)


    except ConnectionException as e:
        print(f"USB Disconnected {e}")

    time.sleep(2)
    client.close()