current community

your communities

more stack exchange communities

Stack Exchange
tour help
Take the 2-minute tour ×
Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It's 100% free, no registration required.
up vote -4 down vote favorite

A 4 bit number , ABCD is a palindrome when A is equal to D and B is equal to C . Draw a circuit to check whether a given 4 bit number is a palindrome or not. Use only 2:1 multiplexers.Do not use any gate. assume complemented inputs are available. I tried but could get circuit using minimum 7 multiplexers .But this circuit is possible using less number of multiplexers. Please can anybody tell how ?

share|improve this question
2  
Yes, but it benefits no one for us to do your homework. –  Ignacio Vazquez-Abrams Oct 20 '13 at 6:36
    
What does a 2:1 multiplexer do? –  jippie Oct 20 '13 at 6:53
    
show your circuit. I can visualize 4 multiplxers as a solution so you need to think a bit harder. –  Andy aka Oct 20 '13 at 7:21
    
This can be done with 3 multiplexers. –  Dave Tweed♦ Oct 20 '13 at 11:20
    
@DaveTweed are they all 2-way devices? –  Andy aka Oct 20 '13 at 15:14

1 Answer 1

up vote 0 down vote

It's been 17 hours now, and I can't tell whether the OP is still interested in this question and its answer, but I'm going to throw out some relevant points without actually giving the final answer.

A 2:1 multiplexer implements the equation Y = S'A + SB, which means that it contains an inverter, two AND gates and an OR gate. This actually makes it a fairly "universal" logic element, and in fact, at least one family of FPGAs uses this concept as its basic building block.

A 2:1 multiplexer can implement a 2-input AND, a 2-input OR or a 1-input NOT directly, and if the complements of the logic inputs are available, it can also do NAND, NOR, XOR and XNOR.

Finally, testing whether two bits are equal is the same as the XNOR operation.

share|improve this answer
    
thing is we cannot use gates.without using gates we have ti implement.give me some hint to implement. –  shivam Oct 21 '13 at 14:37
    
A 2:1 multiplexer has three inputs. Each of those inputs can be tied high, tied low or connected to an input signal or its complement. You should try working out what functions you get from various combinations of those choices. –  Dave Tweed♦ Oct 21 '13 at 15:12

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.