Understanding Programmable Logic Arrays (PLAs)

A Programmable Logic Array (PLA) is a type of programmable logic device used to implement combinational logic circuits. PLAs are often used to realize complex logic functions. They consist of two main parts: a programmable AND gate array and a programmable OR gate array.

Components of a PLA for Combinational Logic

To implement combinational logic functions, a PLA utilizes fundamental logic gates. The structure of a PLA is designed to efficiently implement logic functions in their sum-of-products (SOP) form.

• The first stage is a set of AND gates. This array is programmable, meaning you can choose which input variables (or their complements) are connected to each AND gate. Each AND gate generates a product term (a combination of inputs).
• The second stage is a set of OR gates. This array is also programmable. The outputs of the AND gates (the product terms) can be connected to the inputs of the OR gates. Each OR gate sums up selected product terms to produce the final output logic function.

Therefore, the core components that make up a PLA and are used to implement combinational logic are AND gates and OR gates.

How a PLA Implements Logic Functions

Any combinational logic function can be expressed in sum-of-products form. A PLA's structure directly maps to this form:

• The programmable AND array creates the necessary product terms.
• The programmable OR array sums up the required product terms to generate the desired output functions.

This two-level structure of programmable AND and OR gates makes the PLA a versatile device for implementing various combinational logic circuits based on the required logic equations.

Let's summarize the key components:

Based on the structure and function of a PLA, the components used to implement combinational logic are indeed AND gates and OR gates.