Sunday, July 17, 2011

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.





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