Before Reading Through the pages...
The READER is assumed to have learned the basics of Logic Circuits which is very much essential in the discussions.

Designing with Programmable Logic Devices

Programmable Logic has evolved over the last decade into a design tool permitting digital logic designs with a minimal number of packages and a maximum of flexibility.   The key to PLDs is the use of embedded programmable cells (typically fuse-links) which allow logic components to be configured into specific design field.  This permits logic consolidation with quick implementation and equally quick design revision often without board layout changes.

Design Advantages

Digital Logic designers have always worked under constraints. Reduction of system size and cost demand efficient, compact designs.   System reliability forces designers to compromise between evolving solutions and existing proven methods.  Future revisions demand a degree of flexibility which must be anticipated.  Yet systems themselves increase in complexity, components sophistication requires evermore sophisticated tools and conceiving the optimal design for so many parameters requires a range of skills which must constantly be developed.

PLDs do not solve all this problems. But they do provide a method of dealing with some of the major issues in an effective way by providing a uniform methodology.

• Simplfied System Design - customized applications for PLDs can make systems modular in process making it more easily understandable, without having to study the network of logic device interconnections.

• Increased Functional Density - can provide at least a minimum of 1:4 ratio of chip reduction.

• Security - Since PLDs are programmed by blowing fuses, a security fuse is also a built-in in this device.  Blowing the security fuse prevents re-copying of fusemaps from programmed PLD devices.

• Cost of Upgrade and Modification - In ordinary plain Logic circuit design, a circuit follows a specific requirement.  There are times wherein indirect influences will add a significant change to the overall requirement.  Changing circuits could cost a lot of damage, starting from schematic design to the board level and throwing unused chips back to the drawers.  Redesigning will eat another amount of time for the upgrades.

• Higher Reliability - It has been a rule of thumb that "more parts means more problems" , "less parts means less problem".  A decrease in the number of chips will definitely increase the overall reliability.

RPB