Chapter 1. Tools Utilized
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Figure 5.2: The basic block of a Xilinx XC4000 FPGA
5.2.1
History
FPGAs originated from PROMs and PLDs. The first reprogrammable hardware were
the PROMs. PROM is a non-volatile memory that can be loaded with information.
Different types of PROMs can be either mass programmed at the factory(Mask Pro-
grammable Devices) or by the user(Field programmable). Later came the PLDs that
had a major contribution towards the creation of FPGAs. Although there are several
different types of PLDs, the most common implements a set of fixed logical OR gates
preceded by an array of programmable AND logic gates. Like PROM, PLDs are also
manufactured as both factory programmable and user programmable. These MPLDs
(Mask Programmable Logic Devices) have programmable logic for the AND gates; how-
ever, they are hard-wired between logic gates. In 1985 with the invention of FPGAs,
Xilinx created a device that would not only have programmable gates, but also have
programmable interconnections between gates. The FPGAs were thus simply the next
step in the evolution of PLDs.
Another early field programmable logic device was proposed by Steve Casselman in
1987 to the National Science Foundation. The ideas behind the proposal were to create
a computer chip that used the new technology of programmable gate arrays and was
able to be completely programmed using software. Within the proposed experiment