1. Expand the following: PLA, PAL, CPLD, FPGA.

Answer

PLA - Programmable Logic Array

PAL - Programmable Array Logic

CPLD - Complex Programmable Logic Device

FPGA - Field-Programmable Gate Array

2. Implement the functions: X = A'BC + ABC + A'B'C' and Y = ABC + AB'C using a PLA.

Answer3. What are PLA and PAL? Give the differences between them.

Answer

Programmable Logic Array is a programmable device used to implement combinational logic circuits. The PLA has a set of programmable AND planes, which link to a set of programmable OR planes, which can then be conditionally complemented to produce an output.

PAL is programmable array logic, like PLA, it also has a wide, programmable AND plane. Unlike a PLA, the OR plane is fixed, limiting the number of terms that can be ORed together.

Due to fixed OR plane PAL allows extra space, which is used for other basic logic devices, such as multiplexers, exclusive-ORs, and latches. Most importantly, clocked elements, typically flip-flops, could be included in PALs. PALs are also extremely fast.

4. What is LUT?

Answer

LUT - Look-Up Table. An n-bit look-up table can be implemented with a multiplexer whose select lines are the inputs of the LUT and whose inputs are constants. An n-bit LUT can encode any n-input Boolean function by modeling such functions as truth tables. This is an efficient way of encoding Boolean logic functions, and LUTs with 4-6 bits of input are in fact the key component of modern FPGAs.

5. What is the significance of FPGAs in modern day electronics? (Applications of FPGA.)

Answer- ASIC prototyping: Due to high cost of ASIC chips, the logic of the application is first verified by dumping HDL code in a FPGA. This helps for faster and cheaper testing. Once the logic is verified then they are made into ASICs.
- Very useful in applications that can make use of the massive parallelism offered by their architecture. Example: code breaking, in particular brute-force attack, of cryptographic algorithms.
- FPGAs are sued for computational kernels such as FFT or Convolution instead of a microprocessor.
- Applications include digital signal processing, software-defined radio, aerospace and defense systems, medical imaging, computer vision, speech recognition, cryptography, bio-informatics, computer hardware emulation and a growing range of other areas.

6. What are the differences between CPLD and FPGA.

Answer

7. Compare and contrast FPGA and ASIC digital designing.

Answer8. Give True or False.

(a) CPLD consumes less power per gate when compared to FPGA.

(b) CPLD has more complexity than FPGA

(c) FPGA design is slower than corresponding ASIC design.

(d) FPGA can be used to verify the design before making a ASIC.

(e) PALs have programmable OR plane.

(f) FPGA designs are cheaper than corresponding ASIC, irrespective of design complexity.

Answer

(a) False

(b) False

(c) True

(d) True

(e) False

(f) False

9. Arrange the following in the increasing order of their complexity: FPGA,PLA,CPLD,PAL.

Answer

Increasing order of complexity: PLA, PAL, CPLD, FPGA.

10. Give the FPGA digital design cycle.

Answer
## 2 Comments:

Hi

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Source: Second interview questions

Best regards

Henry

The difference between FPGAs and CPLDs is that FPGAs are internally based on Look-up tables (LUTs) whereas CPLDs form the logic functions with sea-of-gates (e.g. sum of products). CPLDs are meant for simpler designs while FPGAs are meant for more complex designs. In general, CPLDs are a good choice for wide combinational logic applications, whereas FPGAs are more suitable for large state machines (i.e. microprocessors).

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