Decoder is a combinational circuit that has ‘n’ input lines and maximum of 2 n output lines. One of these outputs will be active High based on the combination of inputs present, when the decoder is enabled. That means decoder detects a particular code. The outputs of the decoder are nothing but the min terms of ‘n’ input variables (lines), when it is enabled. 2 to 4 Decoder Let 2 to 4 Decoder has two inputs A 1 & A 0 and four outputs Y 3 , Y 2 , Y 1 & Y 0 . The block diagram of 2 to 4 decoder is shown in the following figure. One of these four outputs will be ‘1’ for each combination of inputs when enable, E is ‘1’. The Truth table of 2 to 4 decoder is shown below. Enable Inputs Outputs E A 1 A 0 Y 3 Y 2 Y 1 Y 0 0 x x 0 0 0 0 1 0 0 0 0 0 1 1 0 1 0 0 1 0 1 1 0 0 1 0 0 1 1 1 1 0 0 0 From Truth table, we can write the Boolean functions for each output as Y 3 = E . A 1 . A 0 Y 3 = E . A ...
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