Digital Electronics: Principles, Devices and Applications

352 Digital ElectronicsQSA1A2A3A4A5A6AZ01001DSFFQQZ1RF1F2F3F4F5F6NZFZQCQRFigure 9.42Quicklogic FPGA logic block.Quicklogic also offers antifuse-based FPGAs, like Actel. They offer two families of devices, namelypASIC and pASIC-2. pASIC-2 is an enhanced version of pASIC. The overall structure is array basedlike the Xilinx FPGAs. The logic blocks are similar to those used in the Actel FPGAs, although morecomplex than their Actel counterparts. Also, each logic block contains a flip-flop. Figure 9.42 showsthe architecture.Review Questions1. How does a programmable logic device differ from a fixed logic device? What are the primaryadvantages of using programmable logic devices?2. Distinguish between a programmable logic array (PLA) device and a programmable array logic(PAL) device in terms of architecture and capability to implement Boolean functions.3. How does a generic array logic (GAL) device differ from its PAL counterpart? Do they differ intheir internal architecture? If yes, then how?4. What are complex programmable logic devices (CPLDs)? Briefly outline salient features of thesedevices and application areas where these devices fit the best.5. How does the architecture of a typical FPGA device differ from that of a CPLD? In what way doesthe architecture affect the timing performance in the two cases?