Xentara skills that are used to collect data from and send control commands to the process are called southbound skills. These skill generally collect measurements and status information from hardware components, and send control commands, setpoints etc. back to the hardware.

Instead of communicating with physical hardware, a southbound skill can also interface with sofware components like, FMUs, AI engines, or process simulation software.

Some examples of southbound skills include:

clients for process communication protocols like EtherCAT, Modbus, or OPC UA. In some protocols, these clients are sometimes referred to as “masters”.
Components for accessing physical hardware components using protocols like SPI, I²C, or the Linux comedi interface
Clients for smart sensors or other smart devices, including things like oscilloscopes
Computer health components that monitor CPU load, network traffic, Disk usage, and the like
AI engines
Processing components like FMUs
Simulators or synthetic data generators

The ultimate goal of a southbound skill is to provide skill data points that allow access to the various physical and virtual input and outputs necessary to monitor and control the process.

Fundamentally, southbound skills are just regular Xentara skills, and are not treated different from other skill. However, most southbound skills follow a unified set of principles and present a unified interface in the form of well-known attributes, events, and tasks.

Southbound skills generally provide three classes of elements: