Write short notes on: i) PLA

Introduction to PLA

Programmable Logic Array (PLA) is a type of digital device that is used to implement combinational logic circuits. The PLA has an array of AND gates and OR gates that can be programmed to achieve the desired logic function. The term "programmable" refers to the ability to define the logic function that the PLA will perform, by programming the presence or absence of connections in the array.

The concept of PLA was first introduced in the early 1970s as a more flexible alternative to the fixed-function logic devices that were commonly used in digital systems at the time. Over the years, PLAs have evolved and improved in terms of speed, capacity, and programmability, making them a key component in many modern digital systems.

Structure of PLA

The basic structure of a PLA consists of three main components: a set of inputs, a set of outputs, and an array of AND and OR gates. The inputs are connected to the AND gates through programmable links, which can be programmed to establish or break the connection between a specific input and a specific AND gate. The outputs of the AND gates are then connected to the OR gates, also through programmable links, to produce the final outputs of the PLA.

Here is a simple diagram illustrating the structure of a PLA:

[Insert Diagram Here]

Working of PLA

The operation of a PLA can be explained in three main steps:

1. Input Processing: The inputs to the PLA are processed through the AND gates. Each AND gate performs a specific logic function on its inputs, determined by the programmed connections. The result is a set of intermediate outputs, each representing a specific combination of the inputs.

2. Output Generation: The intermediate outputs from the AND gates are then processed through the OR gates. Each OR gate performs a specific logic function on its inputs, again determined by the programmed connections. The result is the final outputs of the PLA, each representing a specific combination of the intermediate outputs.

3. Customization: The programmable links in the PLA allow the logic functions performed by the AND and OR gates to be customized. By programming the presence or absence of connections, the PLA can be made to perform any desired logic function on its inputs.

Advantages of PLA

PLAs offer several advantages in digital systems:

1. Flexibility: PLAs are highly flexible, as they can be programmed to perform any desired logic function. This makes them suitable for a wide range of applications in digital systems.

2. Simplicity: PLAs simplify the design of complex logic circuits, as they can implement multiple logic functions in a single device.

3. Efficiency: PLAs can be more efficient than fixed-function logic devices, as they can perform multiple logic functions simultaneously.

Disadvantages of PLA

Despite their advantages, PLAs also have some limitations:

1. Complexity: The programming of PLAs can be complex, especially for large-scale applications.

2. Cost: PLAs can be more expensive than fixed-function logic devices, especially for small-scale applications.

3. Speed: PLAs can be slower than fixed-function logic devices, due to the additional processing required for programmable connections.

Applications of PLA

PLAs are used in a wide range of applications in digital systems, including:

1. Logic Function Implementation: PLAs are commonly used to implement complex logic functions in digital systems, such as arithmetic operations, data encoding and decoding, and control functions.

2. System Integration: PLAs are often used in system integration, where multiple logic functions are combined into a single device to simplify the system design and improve efficiency.

Conclusion

In conclusion, Programmable Logic Array (PLA) is a key component in many digital systems, offering flexibility, simplicity, and efficiency in the implementation of combinational logic circuits. Despite some limitations, the benefits of PLAs often outweigh their drawbacks, making them a valuable tool in digital system design.

Summary

Programmable Logic Array (PLA) is a type of digital device used to implement combinational logic circuits. It consists of inputs, outputs, and an array of AND and OR gates. The inputs are connected to the AND gates through programmable links, and the outputs of the AND gates are connected to the OR gates. The PLA can be programmed to perform any desired logic function on its inputs. PLAs offer flexibility, simplicity, and efficiency in digital system design. They are commonly used for logic function implementation and system integration.

Analogy

A PLA can be compared to a customizable puzzle where the inputs are the puzzle pieces, the AND gates are the puzzle board, and the OR gates are the final picture. By arranging and connecting the puzzle pieces in different ways, you can create different pictures, just like how a PLA can be programmed to perform different logic functions.