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Basic logic functions

07 Jul

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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Posted by on July 7, 2011 in Acadamic

 

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