ABSTRACT
Custom implementations are for circuits needed in large quantities; semicustom for medium quantities, and the programmable logic mode is used for small quantities. To manage costs while exploiting the capabilities of the technology, three implementation approaches are currently employed, based on the quantities of the circuits needed: custom, semicustom, and programmable logic. This chapter provides a brief description of the integrated circuit fabrication process and examines the relative merits of each of these approaches. It also provides details on programmable logic design. The chapter aims to concentrate on design techniques utilizing the four popular PLDs: read only memory, programmable logic array (PLA), programmable array logic and gate arrays (GA). Two types of PLAs are available: mask and field programmable. The static random access memory based field programmableGAs (FPGA) are offered by several manufacturers, including Xilinx, Altera, Atmel, Motorola and AT&T microelectronics. In these FPGAs, logic functions and interconnections are determined by configuration data stored in internal static memory cells.
