TABLE OF CONTENTS Bob Zeidman
Programmable devices have progressed through a long evolution to reach the complexity today to support an entire system on a chip (SOC). This chapter gives an approximately chronological discussion of these devices from least complex to most complex. I say "approximately" because there is definitely overlap between the various devices, which are still in use today. The chapter includes a discussion on application-specific integrated circuits (ASICs) and how CPLDs and FPGAs fit within the spectrum of programmable logic and ASICs.
The objectives of this chapter are to become aware of the different programmable devices available and how they led to the current state-of-the-art device. These objectives are summarized here:
Learn the history of programmable devices.
Obtain a basic knowledge of the technologies of programmable devices.
Understand the architectures of earlier programmable devices.
Discover the speed, power, and density limitations of earlier programmable devices.
Appreciate the needs that arose and that were not addressed by existing devices, and that created a market for CPLDs and FPGAs.
| Note: The ROM cell | The basic diagram for a ROM cell containing a single bit of data is shown in Figure 27.1. The word line is turned on if the address into the chip includes this particular bit cell. The metal layer is used to program the data into the ROM during fabrication. In other words, if the metal layer mask has a connection between the transistor output and the data line, the bit is programmed as a zero. When the bit... |
