Logic Design for Array-Based Circuits
Copyright © 1996, 2001, 2002 Donnamaie E. White
Last Edit July 22, 2001
A semi-custom array, full array or bit-slice design can be upgraded more easily than an LSI/MSI/SSI component or a fixed-instruction set microprocessor design.
For bit-slice, if the design enhancements are known at the time of the original design, allowances can be made through interconnections and functional capabilities that are not accessed until a microprogram accessing these features is incorporated. Many changes can be made with microprogram changes alone.
For semi-custom arrays, if the design enhancements are known in advance, the arrays can be partitioned to leave room for future macro additions or the macro functions could even be incorporated. As with bit-slice, the added capability is simply not accessed until required.
If the design enhancements (evolution) are not known, but are anticipated to occur, the allowances for expansion may be anticipated. The designer may provide room for the design changes to be incorporated onto the older schematics, with additional vectors to be added to the existing simulations. The design is thus easily revised.
The designer must evaluate the all the items discussed in this chapter to make a selection as to the best method of implementation for a specific circuit design. From there, the designer must further evaluate to find the best components available within the chosen category of implementation.
Exercises1. To select a design approach, the following are questions that may need to be answered:
Review these questions. Catalog them as to design-specific, array-specific, component vendor-specific and workstation-specific. What other questions might need to be asked before a design implementation approach (semi-custom, full-custom, fixed components, bit-slice, or gate array) can be selected?
2. Review the latest issues of ASIC News and at least one other ASIC