Programmable Logic Devices (PLD, FPGA, CPLD) Quiz Quiz

Explore your understanding of Programmable Logic Devices, including PLDs, FPGAs, and CPLDs. This quiz covers key architectures, functions, and distinctions essential for mastering digital circuit design and programmable hardware solutions.

1. Understanding PLD Types

   Which statement best distinguishes Complex Programmable Logic Devices (CPLDs) from Field Programmable Gate Arrays (FPGAs) in terms of architecture?

   1. FPGAs are generally limited to simple combinational logic, while CPLDs support rich sequential logic.
   2. CPLDs have a fixed, predictable timing due to their simple internal structure, while FPGAs use a sea-of-gates architecture with less predictable delays.
   3. CPLDs utilize Look-Up Table (LUT) based logic blocks, whereas FPGAs rely on programmable array logic.
   4. CPLDs cannot be reprogrammed after manufacturing, unlike FPGAs.

   Explanation: CPLDs are built with relatively simple, regularly structured logic blocks linked by a global interconnect, leading to more predictable timing compared to FPGAs. FPGAs use a sea-of-gates or LUT-based programmable architecture, which offers high flexibility but can make timing analysis more complex. Option two reverses the typical architecture; FPGAs, not CPLDs, use LUTs. Option three is inaccurate since both CPLDs and FPGAs can handle sequential logic. Option four is wrong because most CPLDs are electrically reprogrammable like FPGAs.

2. Basic PLD Concepts

   In a digital circuit design project requiring frequent updates to the logic functions, which type of programmable device offers the easiest in-system reconfiguration?

   1. Fixed-Function Logic IC
   2. Field Programmable Gate Array (FPGA)
   3. Programmable Array Transistor (PAT)
   4. Mask Programmable Logic Device (MPLD)

   Explanation: FPGAs are specifically designed to support flexible and rapid in-system reconfiguration, making them ideal for projects that require logic to change frequently. Mask Programmable Logic Devices (MPLDs) have their logic fixed at the time of manufacturing and cannot be reconfigured. Fixed-function logic ICs are not programmable at all. Programmable Array Transistor (PAT) is not a commonly recognized type of programmable device.

3. Configuring PLDs

   Which programming technology is commonly used to configure the logic of modern FPGAs and allows for unlimited reprogramming cycles?

   1. SRAM-based configuration
   2. Anti-fuse configuration
   3. PROM-based configuration
   4. Fuse-link configuration

   Explanation: SRAM-based configuration uses static RAM to store the programmable logic, enabling unlimited reprogramming cycles and easy updates to the device's function. PROM-based configurations use programmable read-only memory, which is generally one-time programmable. Fuse-link and anti-fuse configurations are more permanent; anti-fuse is nonvolatile and usually one-time programmable, while fuse-link involves physically blowing fuses. Therefore, the other options do not allow for unlimited or easy reprogramming.

4. PLD Application Scenarios

   A small embedded system requires a programmable logic device to implement simple glue logic and basic control with minimal power consumption. Which type of PLD is most suitable for this application?

   1. Application-Specific Integrated Circuit (ASIC)
   2. Simple Programmable Logic Device (SPLD)
   3. Complex Programmable Logic Device (CPLD)
   4. Field Programmable Gate Array (FPGA)

   Explanation: SPLDs, such as PALs and GALs, are perfect for simple, small-scale logic functions with low power requirements. FPGAs and CPLDs are better suited for complex logic and often consume more power. ASICs are custom-designed for a particular application and are generally not programmable after fabrication, making them unsuitable for glue logic tasks.

5. Logic Structures in PLDs

   In which programmable logic device does each logic cell typically consist of a Look-Up Table (LUT), a D-type flip-flop, and multiplexers for routing logic outputs?

   1. Mask ROM
   2. Field Programmable Gate Array (FPGA)
   3. Complex Programmable Logic Device (CPLD)
   4. Programmable Array Logic (PAL)

   Explanation: FPGAs use logic cells built from LUTs, flip-flops, and multiplexers for flexible logic and routing, supporting a wide range of digital designs. PALs rely on fixed AND-OR structures without LUTs, and CPLDs typically use wider macrocells not based on LUTs. Mask ROMs are not programmable logic devices and lack the structure described in the question.