Basic logic functions

Common functions

·         Comparison

·         Arithmetic

·         Code

·         Encored/decode

·         Data selection

·         Storage

·         Counting

When we are using these components, which are big (bigger than flip-flop) there is less flexibility.

However, using these components provide a quality assurance, where as when we are building with basic components all depend on the ability of the creator.

Comparator

Counter

There are three kinds of counters

1.       Up Counters [counting from 0 to MAX again 0 to MAX]

2.       Down counters [counting from MAX to 0  again MAX to 0]

3.       Up-Down counters [counting 0 to MAX to 0 to MAX …]

These counters again divided in to two categories

1.       Sync

2.       A-sync

With the propagation delay output, do not change at once, as a example

0011 to 0100 happens in three steps

0011 -> 0010 -> 0000 -> 0100 two highlighted parts are not needed here. With these intermediate steps, we cannot use a-sync counters for high-speed operations (have to use sync). Nevertheless, these a-sync ones are easy to build.

Counters as frequency dividers

Data selection function

We can use a multiplexer with a counter to make a programmable frequency divider.