Document structure - References - SIMATIC AX - AX Hardware Engineering documentation - Hardware Engineering,

In an *.hwl.json file, you can define devices, each consisting of one or more modules and IO systems. A module can either be a main module (PLC module or head module) or an IO module (for example a digital input module). In the "Devices" node, you can define a list of modules. One of the modules needs to be a main module (PLC module or head module) of a Profinet IO device. The other modules can for example be IO modules.

You can place the entire hardware configuration in a single document or split it over multiple files. For details, see Using Multiple Files.