# Modbus

1. Test simulation program：[modsim32](https://www.win-tech.com/html/modsim32.htm)
2. Python library used: https://github.com/pymodbus-dev/pymodbus?tab=readme-ov-file

## Usage - Modsim32

1. File > New
2. Connection > Connect > Modbus/TCP Svr
Set the Port `502`
3. Choose **03: HOLDING REGISTER**

## Python Code

"""
Maintainer: Chieh

Work with Modsim3.
Address: 0100
Length: 100
Device ID: 1
03: Holding register
"""

from pymodbus.client.sync import ModbusTcpClient
import random

SERVER_IP = '10.1.2.190'  # aka modbus slave
SERVER_PORT = 502
ADDRESS_START = 100
ADDRESS_LENGTH = 10
DEVICE_ID = 1

client = ModbusTcpClient(host=SERVER_IP, port=SERVER_PORT)
if not client.connect():  # .connect() returns True if connection established
    print("[Error] Fail to connect to modbus slave %s:%d." % (SERVER_IP, SERVER_PORT))
    exit()

res = client.read_holding_registers(address=99, count=10, unit=1)
results = res.registers  # shows the result, type: list
print(results)

# ---------------------------
## write an random value
print("[INFO] Now writing a random boolean value to address= {}.".format(ADDRESS_START))
rand_value = random.randint(10, 19)
print(rand_value)
write_registers_response = client.write_register(
    address=ADDRESS_START, value=rand_value, unit=DEVICE_ID)
write_registers_response.isError()

res = client.read_holding_registers(address=99, count=10, unit=1)
results = res.registers  # shows the result, type: list
print(results)

client.close()

Output:


## Reference

- https://hackmd.io/@quency/most_pymodbus
- https://pymodbus.readthedocs.io/en/latest/source/client.html

---

# Send the string

#!/usr/bin/env python
"""
Pymodbus Payload Building/Decoding Example
--------------------------------------------------------------------------

# Run modbus_payload_server.py or synchronous_server.py to check the behavior
"""
from pymodbus.constants import Endian
from pymodbus.payload import BinaryPayloadDecoder
from pymodbus.payload import BinaryPayloadBuilder
from pymodbus.client.sync import ModbusTcpClient as ModbusClient
from pymodbus.compat import iteritems
from collections import OrderedDict

# --------------------------------------------------------------------------- #
# configure the client logging
# --------------------------------------------------------------------------- #

import logging
FORMAT = ('%(asctime)-15s %(threadName)-15s'
          ' %(levelname)-8s %(module)-15s:%(lineno)-8s %(message)s')
logging.basicConfig(format=FORMAT)
log = logging.getLogger()
log.setLevel(logging.INFO)

ORDER_DICT = {
    "<": "LITTLE",
    ">": "BIG"
}


def run_binary_payload_ex():
    # ----------------------------------------------------------------------- #
    # We are going to use a simple client to send our requests
    # ----------------------------------------------------------------------- #
    client = ModbusClient('192.168.100.217', port=502)
    client.connect()

    # ----------------------------------------------------------------------- #
    # If you need to build a complex message to send, you can use the payload
    # builder to simplify the packing logic.
    #
    # Here we demonstrate packing a random payload layout, unpacked it looks
    # like the following:
    #
    # - an 8 byte string "abcdefgh"
    # - an 8 bit bitstring [0,1,0,1,1,0,1,0]
    # - an 8 bit int -0x12
    # - an 8 bit unsigned int 0x12
    # - a 16 bit int -0x5678
    # - a 16 bit unsigned int 0x1234
    # - a 32 bit int -0x1234
    # - a 32 bit unsigned int 0x12345678
    # - a 16 bit float 12.34
    # - a 16 bit float -12.34
    # - a 32 bit float 22.34
    # - a 32 bit float -22.34
    # - a 64 bit int -0xDEADBEEF
    # - a 64 bit unsigned int 0x12345678DEADBEEF
    # - another 64 bit unsigned int 0x12345678DEADBEEF
    # - a 64 bit float 123.45
    # - a 64 bit float -123.45

    # The packing can also be applied to the word (wordorder) and bytes in each
    # word (byteorder)

    # The wordorder is applicable only for 32 and 64 bit values
    # Lets say we need to write a value 0x12345678 to a 32 bit register

    # The following combinations could be used to write the register

    # +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ #
    # Word Order - Big                      Byte Order - Big
    # word1 =0x1234 word2 = 0x5678

    # Word Order - Big                      Byte Order - Little
    # word1 =0x3412 word2 = 0x7856

    # Word Order - Little                   Byte Order - Big
    # word1 = 0x5678 word2 = 0x1234

    # Word Order - Little                   Byte Order - Little
    # word1 =0x7856 word2 = 0x3412
    # +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ #

    # ----------------------------------------------------------------------- #
    combos = [(wo, bo) for wo in [Endian.Big, Endian.Little]
              for bo in [Endian.Big, Endian.Little]]
    for wo, bo in combos:
        print("-" * 60)
        print("Word Order: {}".format(ORDER_DICT[wo]))
        print("Byte Order: {}".format(ORDER_DICT[bo]))
        print()
        builder = BinaryPayloadBuilder(byteorder=bo,
                                       wordorder=wo)
        strng = "abcdefgh"
        builder.add_string(strng)
        builder.add_bits([0, 1, 0, 1, 1, 0, 1, 0])
        builder.add_8bit_int(-0x12)
        builder.add_8bit_uint(0x12)
        builder.add_16bit_int(-0x5678)
        builder.add_16bit_uint(0x1234)
        builder.add_32bit_int(-0x1234)
        builder.add_32bit_uint(0x12345678)
        builder.add_16bit_float(12.34)
        builder.add_16bit_float(-12.34)
        builder.add_32bit_float(22.34)
        builder.add_32bit_float(-22.34)
        builder.add_64bit_int(-0xDEADBEEF)
        builder.add_64bit_uint(0x12345678DEADBEEF)
        builder.add_64bit_uint(0x12345678DEADBEEF)
        builder.add_64bit_float(123.45)
        builder.add_64bit_float(-123.45)
        payload = builder.to_registers()
        print("-" * 60)
        print("Writing Registers")
        print("-" * 60)
        print(payload)
        print("\n")
        payload = builder.build()
        address = 100
        # Can write registers
        # registers = builder.to_registers()
        # client.write_registers(address, registers, unit=1)

        # Or can write encoded binary string
        client.write_registers(address, payload, skip_encode=True, unit=1)
        # ----------------------------------------------------------------------- #
        # If you need to decode a collection of registers in a weird layout, the
        # payload decoder can help you as well.
        #
        # Here we demonstrate decoding a random register layout, unpacked it looks
        # like the following:
        #
        # - an 8 byte string "abcdefgh"
        # - an 8 bit bitstring [0,1,0,1,1,0,1,0]
        # - an 8 bit int -0x12
        # - an 8 bit unsigned int 0x12
        # - a 16 bit int -0x5678
        # - a 16 bit unsigned int 0x1234
        # - a 32 bit int -0x1234
        # - a 32 bit unsigned int 0x12345678
        # - a 16 bit float 12.34
        # - a 16 bit float -12.34
        # - a 32 bit float 22.34
        # - a 32 bit float -22.34
        # - a 64 bit int -0xDEADBEEF
        # - a 64 bit unsigned int 0x12345678DEADBEEF
        # - another 64 bit unsigned int which we will ignore
        # - a 64 bit float 123.45
        # - a 64 bit float -123.45
        # ----------------------------------------------------------------------- #
        # address = 0x0
        count = len(payload)
        result = client.read_holding_registers(address, count, unit=1)
        print("-" * 60)
        print("Registers")
        print("-" * 60)
        print(result)
        print(result.registers)
        print("\n")
        decoder = BinaryPayloadDecoder.fromRegisters(result.registers,
                                                     byteorder=bo,
                                                     wordorder=wo)

        assert decoder._byteorder == builder._byteorder, \
            "Make sure byteorder is consistent between BinaryPayloadBuilder and BinaryPayloadDecoder"

        assert decoder._wordorder == builder._wordorder, \
            "Make sure wordorder is consistent between BinaryPayloadBuilder and BinaryPayloadDecoder"

        decoded = OrderedDict([
            ('string', decoder.decode_string(len(strng))),
            ('bits', decoder.decode_bits()),
            ('8int', decoder.decode_8bit_int()),
            ('8uint', decoder.decode_8bit_uint()),
            ('16int', decoder.decode_16bit_int()),
            ('16uint', decoder.decode_16bit_uint()),
            ('32int', decoder.decode_32bit_int()),
            ('32uint', decoder.decode_32bit_uint()),
            ('16float', decoder.decode_16bit_float()),
            ('16float2', decoder.decode_16bit_float()),
            ('32float', decoder.decode_32bit_float()),
            ('32float2', decoder.decode_32bit_float()),
            ('64int', decoder.decode_64bit_int()),
            ('64uint', decoder.decode_64bit_uint()),
            ('ignore', decoder.skip_bytes(8)),
            ('64float', decoder.decode_64bit_float()),
            ('64float2', decoder.decode_64bit_float()),
        ])

        print("-" * 60)
        print("Decoded Data")
        print("-" * 60)
        for name, value in iteritems(decoded):
            print("%s\t" % name, hex(value) if isinstance(value, int) else value)

    # ----------------------------------------------------------------------- #
    # close the client
    # ----------------------------------------------------------------------- #
    client.close()


if __name__ == "__main__":
    run_binary_payload_ex()