For very complex systems the state diagram might not be well suited. In this case a tool called the Mnemonic Documented State Diagram or MDS Diagram can incorporate in a more compact way all the complexities of a large system controller.
More information about MDS diagrams can be found in the book An Engineering Approach to Digital Design by William I. Fletcher.
For complex digital logic system with a large number of inputs, the following design methodology, from the point of view of a system controller, can be used:
- State main definitions and specifications of the problem/system
- Define basic operations, limits and restrictions.
- Draw a basic (simplified) block diagram
- Draw a simplified (general) flowchart diagram
- Define the system timing requirement
- Draw a general time diagram
- Detail the controller’s sequential behaviour
- Draw detailed time diagram
- Draw detailed flowchart diagram
- Draw detailed block diagram
- Draw MDS diagram
- Choose the controller architecture: SSI (logic gates and flip-flops), MSI (based on MUXs, …) or LSI (ROM based, …)
- Asign state codes
- Implement the circuit based on the design