TABLE OF CONTENTS The reason for two patterns, equipment modules and control modules (see Figure 5-36) is to provide a structure for reusable elements:
The equipment module pattern for reusable elements with procedural control, using IEC 61131-3 Sequential Function Charts or an equivalent for step-oriented procedures. Procedural control is implicitly sequential in nature, but may have parallel steps and transitions.
The control module pattern for reusable elements with basic control, using IEC 61131-3 Ladder Diagram, Function Block Diagram, Structured Text or an equivalent basic control language for cyclically executed logic loops.
Equipment modules perform minor process actions, and the actions may run to completion and then stop. Equipment modules may directly implement the procedural logic of equipment phases, or they may perform minor process actions for other equipment modules. The reusable elements of equipment modules are equipment phase state and mode management, and recipe-phase to equipment-phase communications.
Control modules perform control actions, setting or reading equipment states and generally maintaining steady-state or cyclic control.
