Design 5 to 32 Decoder using 3 to 8 Decoder


👤 Diwas Poudel    🕒 Dec 12 2021    📁 Fix    📜 0 comment

Let's learn about decoders and their applications before designing 5 to 32 decoders with 3 to 8 decoders.

The decoder is a set of circuits that performs the opposite function of Encoder. It has a large number of input and output lines, but no selection lines such as MUX and DEMUX.

To communicate between two devices, many communication projects use decoders. It is found in microprocessors, microcontrollers, memory chips, and other electronic devices.

Sometimes this design is necessary because in the market we may not get 5 to 32 decoders and we are forced to design it with only available 3 to 8 Decoder.

Designing 5 * 32 Decoder using 3 * 8 Decoder

In 5* 32 Decoder we have 5 input lines and 32 output lines and will just select one output line based on various input combinations.

In 3 * 8 Decoder we have 3 input lines and 8 output lines and will just select one output line based on various input combinations.

Altogether 5  3 to 8 decoders are required to produce 32 output lines of 5 to 32 decoders. But note that among 4 decoders present on the right side only one decoder is active at a time and one decoder response to the result.

Circuit Diagram for implementing 3 to 8 decoder using 5 to 32 decoder:

implement-5-to-32-decoder-using-3-to-8-decoder

Decoder Enable Logic

Decoder Enable Logic is as follows:

ABCDE Decoder Enabled
000XX D1
001XX D2
010XX D3
011XX D4

ie.

Here, A is always 0 as it is grounded.

  • When A = 0 , B = 0 ,C = 0, DE( any 00 or 01 or 10 or 11) , D1 Decoder is selected. 
  • When A = 0 , B = 0,C =1 , DE( any 00 or 01 or 10 or 11) , D2 Decoder is selected. 
  • When A = 0 , B = 1 ,C=0, DE( any 00 or 01 or 10 or 11) , D3 Decoder is selected. 
  • When A = 0 , B = 1,C = 1 ,DE( any 00 or 01 or 10 or 11) , D4 Decoder is selected. 

This concludes that selecting Decoder (D1, D2, D3, D4) only depends on the D5 decoder.