PyADS example

An overview of PyADS features showing some basic features.

Python

The following is shown:

• Connecting to an existing plc
• Getting an overview of existing symbols
• Unstructured variables
  • Reading
  • Writing
• Structured variables
  • Structure definition
  • Reading
  • Writing
• Symbol callback that prints the information every time the value is changed

An environment.yml file is provided to help initialise the conda environment used to run the script. Create the new environment using

conda env create -f environment.yml

then activate the environment with

conda activate pyads-example

The script accepts two command line arguments -a\--AmsNetID =default> local, which accepts an AmsNetID.
And -n\--num_heartbeat =deafult> 3, which allows you to set how many times the heartbeat variable is read and printed.

An example call is

python communicate_over_ads.py -a 5.95.0.12.1.1 -n 4

TwinCAT

The TwinCAT project simply holds a few variables iHeartbeat, which is simply a counter that indicates PLC health. and a structured data type with the following definition

Make sure to add {attribute 'pack_mode' := '1'}, which is expected by pyads for correct byte alignment.

Just activate the test PLC on a target device and make note of the AmsNetID to use when calling the provided python script.

Software versions used

• python = 3.9
• TwinCAT = 3.1.4024.47

Resources:

• PyADS: stlehmann/pyads
• Beckhoff ADS documentation: Infosys

This code is purely for demonstrative purposes as to how to interact with the library (and the underlying system). It is not a programming example to implement dierectly, and does not reflect correct coding practices.