Usage

Overview to use and test this micropython-modbus library

---

Note

The onwards described steps assume a successful setup as described in the setup chapter

MicroPython

This section describes the necessary steps on the MicroPython device to get ready to test and run the examples.

# Linux/Mac
source .venv/bin/activate

rshell -p /dev/tty.SLAB_USBtoUART --editor nano

On a Windows based system activate the virtual environment and enter the remote shell like this

.venv\Scripts\activate.bat

rshell -p COM9

The onwards mentioned commands shall be performed inside the previously entered remote shell.

Register configuration

The available registers can be defined by a JSON file, placed inside the /pyboard/registers folder or any other location on the board and loaded in main.py or by defining a dictionary.

As an example the registers of a brainelectronics MyEVSE, MyEVSE on Tindie board and others are provided with this repo.

Structure

If only an interaction with a single register is intended no dictionary needs to be defined of course. The onwards explanations assume a bigger setup of registers on the same target/client/slave device.

The JSON file/dictionary shall follow the following pattern/structure

{
    "COILS": {          # this key shall contain all coils
        "COIL_NAME": {  # custom name of a coil
            "register": 42,     # register address of the coil
            "len": 1,           # amount of registers to request aka quantity
            "val": 0,           # used to set a register
            # the onwards mentioned keys are optional
            "description": "Optional description of the coil",
            "range": "[0, 1]",  # may provide a range of the value, only for documentation purpose
            "unit": "BOOL"      # may provide a unit of the value, only for documentation purpose
        }
    },
    "HREGS": {          # this key shall contain all holding registers
        "HREG_NAME": {  # custom name of a holding register
            "register": 93,     # register address of the holding register
            "len": 1,           # amount of registers to request aka quantity
            "val": 19,          # used to set a register
            "description": "Optional description of the holding register",
            "range": "[0, 65535]",
            "unit": "Hz"
        },
    },
    "ISTS": {           # this key shall contain all static input registers
        "ISTS_NAME": {  # custom name of a static input register
            "register": 67,     # register address of the static input register
            "len": 1,           # amount of registers to request aka quantity
            "val": 0,           # used to set a register, not possible for ISTS
            "description": "Optional description of the static input register",
            "range": "[0, 1]",
            "unit": "activated"
        }
    },
    "IREGS": {          # this key shall contain all input registers
        "IREG_NAME": {  # custom name of an input register
            "register": 10,     # register address of the input register
            "len": 1,           # amount of registers to request aka quantity
            "val": 60001,       # used to set a register, not possible for IREGS
            "description": "Optional description of the static input register",
            "range": "[0, 65535]",
            "unit": "millivolt"
        }
    }
}

If not all register types are used they can be of course removed from the JSON file/dictionary. The smallest possible definition for reading a coil would look like

{
    "COILS": {          # this key shall contain all coils
        "COIL_NAME": {  # custom name of a coil
            "register": 42,     # register address of the coil
            "len": 1            # amount of registers to request aka quantity
        }
    }
}

In order to act as client/slave device the same structure can be used. If no val element is found in the structure the default values are

Type	Function Code	Default value
COILS	0x01	False (0x0)
ISTS	0x02	False (0x0)
HREGS	0x03	0
IREGS	0x04	0

The value of multiple registers can be set like this

{
    "HREGS": {          # this key shall contain all holding registers
        "HREG_NAME": {  # custom name of a holding register
            "register": 93,     # register address of the holding register
            "len": 3,           # amount of registers to request aka quantity
            "val": [29, 38, 0]  # used to set a register
        }
    }
}

Warning

As of version 2.0.0 of this package it is not possible to request only the holding register 94, which would hold 38 in the above example.

This is a bug (non implemented feature) of the client/slave implementation. For further details check issue #35

Detailed key explanation

The onwards described key explanations are valid for COIL, HREG, IST and IREG

Register

The key register defines the register to request or manipulate.

According to the Modbus specification the register address has to be in the range of 0x0000 to 0xFFFF (65535) to be valid.

Length

The key len defines the amout of registers to be requested starting from/with the defined register address.

According to the Modbus specification the length or amount depends on the type of the register as summarized in the table below.

Type	Function Code	Valid range
COILS	0x01	0x1 to 0x7D0 (2000)
ISTS	0x02	0x1 to 0x7D0 (2000)
HREGS	0x03	0x1 to 0x7D (125)
IREGS	0x04	0x1 to 0x7D (125)

In order to read 5 coils starting at 124 use the following dictionary aka config

{
    "COILS": {          # this key shall contain all coils
        "COIL_NAME": {  # custom name of a coil
            "register": 124,    # register address of the coil
            "len": 5            # amount of registers to request aka quantity
        }
    }
}

The output will be a list of 5 elements like [True, False, False, True, True] depending on the actual device coil states of course.

Value

The key val defines the value of registers to be set on the target/client device.

According to the Modbus specification the value (range) depends on the type of the register as summarized in the table below.

Type	Function Code	Valid value	Comment
COILS	0x05	0x0000 or 0xFF00	This package maps 0 or False to 0x0000 and 1 or True to 0xFF00
HREGS	0x06	0x0000 to 0xFFFF (65535)

Optional description

The optional key description can be used to provide an additional description of the register. This might be helpful if the register name is not meaninful enough or for any other reason of course.

Optional range

The optional key range can be used to indicate the possible value range of this specific target. For example a holding register for setting a PWM output might only support a range of 0 to 100. This might be especially helpful with the optional unit key.

Optional unit

The optional key unit can be used to provide further details about the unit of the register. In case of the PWM output register example of the optional range key the recommended value for this key could be percent.

Register usage

This section describes the usage of the following available functions

• 0x01 read_coils

• 0x02 read_discrete_inputs

• 0x03 read_holding_registers

• 0x04 read_input_registers

• 0x05 write_single_coil

• 0x06 write_single_register

• 0x0F write_multiple_coils

• 0x10 write_multiple_registers

based on TCP togehter with the latest provided examples

All described functions require a successful setup of a Host communicating to/with a Client device which is providing the data and accepting the new data.

from umodbus.tcp import TCP as ModbusTCPMaster

slave_tcp_port = 502            # port to listen to
slave_addr = 10                 # bus address of client
slave_ip = '192.168.178.69'     # IP address, to be adjusted

host = ModbusTCPMaster(
    slave_ip=slave_ip,
    slave_port=slave_tcp_port,
    timeout=5)                  # optional, default 5

Coils

Coils represent binary states, which can be get as and set to either 0 (off) or 1 (on).

Read

Note

The function code 0x01 is used to read from 1 to 2000 contiguous status of coils in a remote device.

With the function read_coils a single coil status can be read.

coil_address = 125
coil_qty = 2
coil_status = host.read_coils(
    slave_addr=slave_addr,
    starting_addr=coil_address,
    coil_qty=coil_qty)
print('Status of COIL {}: {}'.format(coil_address, coil_status))
# Status of COIL 125:  [True, False]

Warning

Please be aware of bug #35.

It is not possible to read a specific position within a configured list of multiple coils on a MicroPython Modbus TCP client device. Reading coil 126 in the above example will throw an error.

This bug affects only devices using this package. Other devices work as expected and can be addressed as specified.

Write

Coils can be set with False or 0 to the OFF state and with True or 1 to the ON state.

Single

Note

The function code 0x05 is used to write a single output to either ON or OFF in a remote device.

With the function write_single_coil a single coil status can be set.

coil_address = 123
new_coil_val = 0
operation_status = host.write_single_coil(
    slave_addr=slave_addr,
    output_address=coil_address,
    output_value=new_coil_val)
print('Result of setting COIL {}: {}'.format(coil_address, operation_status))
# Result of setting COIL 123: True

Warning

Please be aware of bug #15.

It is not possible to write to a specific position within a configured list of multiple coils on a MicroPython Modbus TCP client device.

This bug affects only devices using this package. Other devices work as expected and can be addressed as specified.

Multiple

Note

The function code 0x0F is used to force each coil in a sequence of coils to either ON or OFF in a remote device.

With the function write_multiple_coils multiple coil states can be set at once.

coil_address = 126
new_coil_vals = [1, 1, 0]
operation_status = self._host.write_multiple_coils(
            slave_addr=slave_addr,
            starting_address=coil_address,
            output_values=new_coil_vals)
print('Result of setting COIL {}: {}'.format(coil_address, operation_status))
# Result of setting COIL 126: True

Warning

Please be aware of bug #35.

It is not possible to write to a specific position within a configured list of multiple coils on a MicroPython Modbus TCP client device. Setting coil 127, which is 1 in the above example will throw an error.

This bug affects only devices using this package. Other devices work as expected and can be addressed as specified.

Discrete inputs

Discrete inputs represent binary states, which can be get as either 0 (off) or 1 (on). Unlike coils, these cannot be set.

Read

Note

The function code 0x02 is used to read from 1 to 2000 contiguous status of discrete inputs in a remote device.

With the function read_discrete_inputs discrete inputs can be read.

ist_address = 68
input_qty = 2
input_status = host.read_discrete_inputs(
    slave_addr=slave_addr,
    starting_addr=ist_address,
    input_qty=input_qty)
print('Status of IST {}: {}'.format(ist_address, input_status))
# Status of IST 68: [True, False]

Holding registers

Holding registers can be get as and set to any value between 0 and 65535. If supported by the client device, data can be marked as signed values to represent -32768 through 32767.

Read

Note

The function code 0x03 is used to read the contents of a contiguous block of holding registers in a remote device.

With the function read_holding_registers a single holding register can be read.

hreg_address = 94
register_qty = 3
register_value = host.read_holding_registers(
    slave_addr=slave_addr,
    starting_addr=hreg_address,
    register_qty=register_qty,
    signed=False)
print('Status of HREG {}: {}'.format(hreg_address, register_value))
# Status of HREG 94: [29, 38, 0]

Warning

Please be aware of bug #35.

It is not possible to read a specific position within a configured list of multiple holding registers on a MicroPython Modbus TCP client device. Reading holding register 95, holding the value 38 in the above example will throw an error.

This bug affects only devices using this package. Other devices work as expected and can be addressed as specified.

Write

Holding registers can be set to 0 through 65535 or -32768 through 32767 in case signed values are used.

Single

Note

The function code 0x06 is used to write a single holding register in a remote device.

With the function write_single_register a single holding register can be set.

hreg_address = 93
new_hreg_val = 44
operation_status = host.write_single_register(
    slave_addr=slave_addr,
    register_address=hreg_address,
    register_value=new_hreg_val,
    signed=False)
print('Result of setting HREG {}: {}'.format(hreg_address, operation_status))
# Result of setting HREG 93: True

Multiple

Note

The function code 0x10 is used to write a block of contiguous registers (1 to 123 registers) in a remote device.

With the function write_multiple_registers holding register can be set at once.

hreg_address = 94
new_hreg_vals = [54, -12, 30001]
operation_status = self._host.write_multiple_registers(
    slave_addr=slave_addr,
    starting_address=hreg_address,
    register_values=new_hreg_vals,
    signed=True)
print('Result of setting HREG {}: {}'.format(hreg_address, operation_status))
# Result of setting HREG 94: True

Warning

Please be aware of bug #35.

It is not possible to write to a specific position within a configured list of multiple holding registers on a MicroPython Modbus TCP client device. Setting holding register 95 + 96 to e.g. [-12, 30001] in the above example will throw an error.

This bug affects only devices using this package. Other devices work as expected and can be addressed as specified.

Input registers

Input registers can hold values between 0 and 65535. If supported by the client device, data can be marked as signed values to represent -32768 through 32767. Unlike holding registers, these cannot be set.

Read

Note

The function code 0x04 is used to read from 1 to 125 contiguous input registers in a remote device.

With the function read_input_registers input registers can be read.

ireg_address = 11
register_qty = 3
register_value = host.read_input_registers(
    slave_addr=slave_addr,
    starting_addr=ireg_address,
    register_qty=register_qty,
    signed=False)
print('Status of IREG {}: {}'.format(ireg_address, register_value))
# Status of IREG 11: [59123, 0, 390]

TCP

Get two network capable boards up and running, collecting and setting data on each other.

Adjust the WiFi network name (SSID) and password to be able to connect to your personal network or remove that section if a wired network connection is used.

Client

The client, former known as slave, provides some dummy registers which can be read and updated by another device.

cp examples/tcp_client_example.py /pyboard/main.py
cp examples/boot.py /pyboard/boot.py
repl

Inside the REPL press CTRL+D to perform a soft reboot. The device will serve several registers now. The log output might look similar to this

MPY: soft reboot
System booted successfully!
Waiting for WiFi connection...
Waiting for WiFi connection...
Connected to WiFi.
('192.168.178.69', '255.255.255.0', '192.168.178.1', '192.168.178.1')
Setting up registers ...
Register setup done
Serving as TCP client on 192.168.178.69:502

Host

The host, former known as master, requests and updates some dummy registers of another device.

cp examples/tcp_host_example.py /pyboard/main.py
cp examples/boot.py /pyboard/boot.py
repl

Inside the REPL press CTRL+D to perform a soft reboot. The device will request and update registers of the Client after a few seconds. The log output might look similar to this

MPY: soft reboot
System booted successfully!
Waiting for WiFi connection...
Waiting for WiFi connection...
Connected to WiFi.
('192.168.178.42', '255.255.255.0', '192.168.178.1', '192.168.178.1')
Requesting and updating data on TCP client at 192.168.178.69:502

Status of COIL 123: [True, False, False, False, False, False, False, False]
Result of setting COIL 123: True
Status of COIL 123: [False, False, False, False, False, False, False, False]

Status of HREG 93: (44,)
Result of setting HREG 93: True
Status of HREG 93: (44,)

Status of IST 67: [False, False, False, False, False, False, False, False]
Status of IREG 10: (60001,)

Finished requesting/setting data on client
MicroPython v1.18 on 2022-01-17; ESP32 module (spiram) with ESP32
Type "help()" for more information.
>>>

TCP-RTU bridge

This example implementation shows how to act as bridge between an RTU (serial) connected device and another external TCP device.

For further details about a TCP-RTU bridge implementation check the header comment of main.py.

Classic development environment

This section describes the necessary steps on the computer to get ready to test and run the examples.

# Linux/Mac
source .venv/bin/activate

On a Windows based system activate the virtual environment like this

.venv\Scripts\activate.bat

The onwards mentioned commands shall be performed inside the previously activated virtual environment.

TCP

Read and write the Modbus register data from a MicroPython device with the brainelectronics ModbusWrapper provided with the modules submodule

Read data

python modules/read_device_info_registers.py \
--file=registers/example.json \
--connection=tcp \
--address=192.168.178.69 \
--port=502 \
--print \
--pretty \
--debug \
--verbose=3

Or use the even more convenient wrapper script for the wrapper.

cd examples
sh read_registers_tcp.sh 192.168.178.69 ../registers/example.json 502

Write data

python modules/write_device_info_registers.py \
--file=registers/set-example.json \
--connection=tcp \
--address=192.168.178.69 \
--port=502 \
--print \
--pretty \
--debug \
--verbose=3

Or use the even more convenient wrapper script for the wrapper.

cd examples
sh write_registers_tcp.sh 192.168.178.69 ../registers/set-example.json 502

Docker development environment

Pull container

Checkout the available MicroPython containers

docker pull micropython/unix:v1.18

Spin up container

Simple container

Use this command for your first tests or to run some MicroPython commands in a simple REPL

docker run -it \
--name micropython-1.18 \
--network=host \
--entrypoint bash \
micropython/unix:v1.18

Enter MicroPython REPL

Inside the container enter the REPL by running micropython-dev. The console should now look similar to this

root@debian:/home#
MicroPython v1.18 on 2022-01-17; linux version
Use Ctrl-D to exit, Ctrl-E for paste mode
>>>

Manually run unittests

In order to manually execute only a specific set of tests use the following command inside the container

# run all unittests defined in "tests" directory and exit with status result
micropython-dev -c "import unittest; unittest.main('tests')"

# run all tests of "TestAbsoluteTruth" defined in tests/test_absolute_truth.py
# and exit with status result
micropython-dev -c "import unittest; unittest.main(name='tests.test_absolute_truth', fromlist=['TestAbsoluteTruth'])"

Custom container for unittests

docker build \
--tag micropython-test \
--file Dockerfile.tests .

The unittests are executed during the building process. It will exit with a non-zero status in case of a unittest failure.

The return value can be collected by echo $? (on Linux based systems), which will be either 0 in case all tests passed, or 1 if one or multiple tests failed.

Docker compose

The following command uses the setup defined in the docker-compose.yaml file to act as two MicroPython devices communicating via TCP. The container micropython-host defined by Dockerfile.host acts as host and sets/gets data at/from the client as defined by tcp_host_example.py. On the other hand the container micropython-client defined by Dockerfile.client acts as client and provides data for the host as defined by tcp_client_example.py. The port defined in tcp_host_example.py and tcp_client_example.py has to be open and optionally exposed in the docker-compose.yaml file.

docker compose up --build --exit-code-from micropython-host

The option --build can be skipped on the second run, to avoid rebuilds of the containers. All “dynamic” data is shared via volumes

Test for TCP example

docker compose -f docker-compose-tcp-test.yaml up --build --exit-code-from micropython-host

Documentation

The documentation is automatically generated on every merge to the develop branch and available here

Install required packages

# create and activate virtual environment
python3 -m venv .venv
source .venv/bin/activate

# install and upgrade required packages
pip install -U -r docs/requirements.txt

Create documentation

Some usefull checks have been disabled in the docs/conf.py file. Please check the documentation build output locally before opening a PR.

# perform link checks
sphinx-build docs/ docs/build/linkcheck -d docs/build/docs_doctree/ --color -blinkcheck -j auto -W

# create documentation
sphinx-build docs/ docs/build/html/ -d docs/build/docs_doctree/ --color -bhtml -j auto -W

The created documentation can be found at docs/build/html.