Software Module Specifications provide the details of various the modules of overal system
Most Process Automation systems are implemented using DCS or PLC based systems
These generally have a collection of standard reusable modules that need to be configured and/or programmed, the modules specs should provide detail of this along with examples of code.
What sort of modules does a process automation system have?
Examples are
Control Modules such as PID Loops, Indicators etc
HMI Graphic displays
Equipment Basic Control
Phase Logic
Operations
Unit Procedures
Recipes
Note that DCS and some PLC sytems provide extensive inherent functions to handle such things as scanning inputs and setting outputs, some fault detection, communications etc. A SMS does not really need to define these as they are part of thee standard system.