Quickstart

Modpoll is a tool for communication with Modbus devices, so ideally it makes more sense if you have a real modbus device on hand for the following test, but it is OK if you don’t, we have deployed a virtual Modbus TCP device on cloud at modsim.topmaker.net:502, the code is available in my another project modsim, let’s start expoloring modpoll tool with the virtual device modsim.

Test with modsim

modsim is a very simple Modbus TCP device simulator deployed on cloud, it populates the first 100 registers for each type of Coil / Discrete input / Input register / Holding register,

modsim register configuration

Object type	Access	Size	Address Space
Coil	Read-write	1 bit	1-100
Discrete Input	Read-only	1 bit	10001-10100
Input Register	Read-only	16 bits	30001-30100
Holding Register	Read-write	16 bits	40001-40100

Using modpoll tool, you can poll the first 5 holding registers via the following command,

modpoll --tcp modsim.topmaker.net --config https://raw.githubusercontent.com/gavinying/modpoll/master/examples/modsim.csv

or run modpoll in docker,

docker run topmaker/modpoll modpoll --tcp modsim.topmaker.net --config https://raw.githubusercontent.com/gavinying/modpoll/master/examples/modsim.csv

Meanwhile, if you prefer a local test or simply failed to connect to online modsim service, you can always launch your own device simulator via the following command,

docker run -p 5020:5020 topmaker/modsim

It will simulate a Modbus TCP device running at localhost:5020, and you shall be able to connect it via the following command,

modpoll --tcp localhost --tcp-port 5020 --config https://raw.githubusercontent.com/gavinying/modpoll/master/examples/modsim.csv