Up Down Counter in Digital Electronics

A counter which can be made to count in either the forward or reverse direction is called an up-down, a reversible or forward-backward counter.

Down Counter

A binary counter with a reverse count is called a binary down counter. In a down counter, the binary counter is decremented by 1 with every input count pulse. The count of a 4-bit down counter starts from binary 15 and continues to binary counts 14, 13, 12… 0 and then back to 15. In a binary down counter, outputs are taken from the complement terminals Q’ of all flip flops.

For a down counter, when Q goes from 0 to 1, Q’ will go from 1 to 0 and complement the next flip flop.

Up Counter

A binary counter with a normal count is called a binary up counter. In a up counter, the binary counter is incremented by 1 with every input clock pulse. Outputs are taken drom the normal output terminal Q of all flip flops. For a up counter when Q goes from 1 to 0, it complements the next flip flop.

Up Down counter in digital electronics

In above diagram, mode control line is also called up down counter line.

When mode control line is 1, all gates labeled as 1 will be enabled and all gates labeled as 2 will be disabled. The counter works like a Up Counter.

When mode control line is 0, all gates labeled as 1 will be disabled and all gates labeles as 1 will be enabled. The counter works like a Down Counter.

CLK Q2 Q1 Q0 Q0 Q1 Q2
0 0 0 0 1 1 1
1 1 1 1 0 0 0
2 1 1 0 1 0 0
3 1 0 1 0 1 0
4 1 0 0 1 1 0
5 0 1 1 0 0 1
6 0 1 0 1 0 1
7 0 0 1 0 1 1
8 0 0 0 1 1 1

 

 

 

 

Leave a Reply

Your email address will not be published. Required fields are marked *

*

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code class="" title="" data-url=""> <del datetime=""> <em> <i> <q cite=""> <strike> <strong> <pre class="" title="" data-url=""> <span class="" title="" data-url="">