Chapter 8

Writing Circuit Descriptions

To understand Foundation Express and to write VHDL descriptions that produce efficient synthesized circuits, study the information presented in the following sections of this chapter.

• “How Statements Are Mapped to Logic”
  
  
• “Asynchronous Designs”
  
  
• “Don't Care Inference”
  
  
• “Synthesis Issues”
  
  

Here are some general guidelines for writing efficient circuit descriptions:

• Restructure a design that makes repeated use of several large components, to minimize the number of instantiations.
  
  
• In a design that needs some, but not all, of its variables or signals stored during operation, minimize the number of latches or flip-flops required.
  
  
• Consider collapsing hierarchy for more efficient synthesis.