34 votes 34 votes How many $3$-to-$8$ line decoders with an enable input are needed to construct a $6$-to-$64$ line decoder without using any other logic gates? $7$ $8$ $9$ $10$ Digital Logic gatecse-2007 digital-logic normal isro2011 decoder + – Kathleen asked Sep 21, 2014 • edited Oct 31, 2018 by kenzou Kathleen 21.3k views answer comment Share Follow See 1 comment See all 1 1 comment reply shree commented Jan 2, 2015 reply Follow Share @Arjun Sir, please help to solve these type of questions. 0 votes 0 votes Please log in or register to add a comment.
Best answer 59 votes 59 votes Answer is C: To get $6:64$ we need $64$ $o/p$ We have $3:8$ decode with $8$ $o/p$. So, we need $64/8=8$ decoders. Now, to select any of this $8$ decoder we need one more decoder. Total$=$ $8+1= 9$ decoders jayendra answered Jan 2, 2015 • edited Jun 25, 2018 by Milicevic3306 jayendra comment Share Follow See all 7 Comments See all 7 7 Comments reply anshu commented Feb 6, 2015 reply Follow Share But then it should be called 3-64 decoder where is the six ?? 5 votes 5 votes partha sarkar commented Jun 21, 2016 reply Follow Share When the first decoder will select any one of the 8 decoders attached with their enable lines then rest of the decoder will not be counted and first decoder will have 3 inputs leaving enable line and the second decoder will have remaining 3 line hence, 6 inputs 23 votes 23 votes Tuhin Dutta commented Sep 5, 2017 reply Follow Share Please explain with a diagram 0 votes 0 votes Rishabh Gupta 2 commented Oct 9, 2017 reply Follow Share If still not clear, here's the diagram just for you :) 80 votes 80 votes Anubhav Kaushik commented Dec 2, 2017 reply Follow Share Correct as the output depends on 6 inputs 0 votes 0 votes Sourav Basu commented Feb 25, 2018 reply Follow Share I0, I1, I2 are most significant bits( input sequence- I0 I1 I2 I3 I4 I5 ) 0 votes 0 votes once_2019 commented Jun 17, 2018 reply Follow Share conceptual answer @partha sarkar 0 votes 0 votes Please log in or register to add a comment.
26 votes 26 votes Answer : C In first Level we need 64 / 8 = 8 Decoder In second Level to cover 8 select lines Which are coming out from 8 decoder we need 8 / 8 = 1 Decoder Total =8+1= 9 decoders shekhar chauhan answered Jun 21, 2016 shekhar chauhan comment Share Follow See all 2 Comments See all 2 2 Comments reply shekhar chauhan commented Jun 25, 2016 reply Follow Share Can someone explain what I have written wrong in this Answer .I have got a downvote on it .Whoever gave it (downvote) please explain the correct method to solve it along with answer... 2 votes 2 votes shivanisrivarshini commented Jun 25, 2016 reply Follow Share I think Ur not wrong 2 votes 2 votes Please log in or register to add a comment.
19 votes 19 votes Quickest way to solve this type of problems will b: Number of m bit MUX/DeMUX/Decoder/Encoder to construct N bit MUX/DeMUX/Decoder/Encoder is: ceil (N-1)/(M-1) In given problem, (N-1)/(M-1)= 64-1/8-1 =63/7 =9 sh!va answered May 2, 2017 sh!va comment Share Follow See all 4 Comments See all 4 4 Comments reply lambda commented Jan 26, 2018 reply Follow Share Is this formula really true. Where does it come from, give some reference man. 3 votes 3 votes Lakshman Bhaiya commented Oct 4, 2019 reply Follow Share Ref:https://www.quora.com/How-do-I-implement-a-6-to-64-line-decoder-using-3-to-8-line-decoders-only 6 votes 6 votes raja11sep commented Sep 14, 2022 reply Follow Share @Deepak Poonia sir is this formula correct? 0 votes 0 votes Digvi_sp commented Jul 25, 2023 reply Follow Share this formula is not correct, because a 4x16 decoder can be constructed from only 2 3x8 decoders with enable input 0 votes 0 votes Please log in or register to add a comment.
1 votes 1 votes Answer - (C) 9 In general to construct a log2m x m decoder using log2n x n decoders, Number of levels needed, k = ceil(lognm) Total number of devices needed = ((m)/(n-1))*(1-1/Nk) Here m=64 and n=8. So k =2 and no. of devices = 9. [log2n means logn base 2, similarly lognm means logm base n] vaibhavkedia968 answered Jan 26, 2020 vaibhavkedia968 comment Share Follow See all 0 reply Please log in or register to add a comment.