ModTerm 1.3.0

A modbus analyser written in pure Python

ModTerm

Introduction

ModTerm is a terminal based modbus analyser software, written in pure Python, utilising the curses UI extensions. The aim of the software is to help reverse engineering modbus data of unknown, or poorly documented modbus devices and allow registers to be written into the devices for testing and analysis purposes.

Features

Reading registers

ModBus registers can be read from devices connected to the computer via TCP or RTU. The registers read from the device are listed in a table, with the rows being the register numbers, and the columns being results of various register decoding methods, such as INT16, INT32, Float32, string, bits, etc. The endianness can be changed on the fly to make sense of the register contents. Supports reading registers in blocks, if the number of registers to be read is above the specified block size (maximum of 125 registers per block as per modbus specification), the reads are broken down to blocks of register reads as per block size specified. Reading registers individually one by one can be achieved by setting the block size to 1.

Writing registers

Registers with a provided encoding method can be written into the required number of registers. When the multicast option is enabled, the register write operation is sent to unit ID 0 (regardless of the defined unit ID) and no response is expected.

Scanning devices on a bus

This feature allows to sweep through modbus unit IDs on a connected bus and run a register read operation, in the hope of receiving a response and thus detecting a device.

Requirements

The project runs best on Python 3.11 and above, but should run on any versions of Python above 3.9.

It depends on and uses the pymodbus and pyserial libraries, which should be collected by pip, from pypi during installation. Please visit and support these free and open source projects!

• pymodbus: https://github.com/pymodbus-dev/pymodbus
• pyserial: https://github.com/pyserial/pyserial

⚠️ Modterm has been tested on macOS and Linux, but not on Windows. According to the documentation of the curses module in Python, it is not included in the Windows version. The documentation mentions the UniCurses module to be used under Windows, but this has not been tested yet. This section will be updated once testing has been done. For Windows users wanting to take advantage of this software, I recommend using WSL.

Installation and usage

• Install a version of Python 3 using your operating system's package manager, or start up a virtual environment with Python version being ideally 3.11 or above
• Issue pip3 install modterm
• Launch the app by issuing modterm in the terminal.

The menu items and configuration options are accessible via the F-keys indicated next to each option. On the main screen, pressing F1 brings up the help screen to show which features are accessible via which keys.

Ways to contribute

For now, please report any issues with decoding, inconsistencies, bugs and crashes.

Feel free to suggest improvements and changes that would help

Development roadmap

The below describes the features planned to be added for each point release in the future. All the below are subject to change

V1.1

• Add coil and discrete input reads/writes (where applicable)
• Sweep IP addresses for ModbusTCP responses

V1.2

• Write float registers
• Test windows compatibility

V1.3

• Read modbus device information registers