All About Circuits Forum How to use a 8-bit multiplexer
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#1
09-10-2006, 12:30 PM
 yjpang84 New Member Join Date: Sep 2006 Posts: 1
How to use a 8-bit multiplexer

Guys im desperate..

this is the qn: Z is a boolean function of 3 input variables A,B and C. If A=C; else Z=0.

Design and draw a clearly labelled diagram to implement Z using only one 8-bit multiplexer.

i don't even understand the question. please enlighten.
#2
09-10-2006, 03:02 PM
 thingmaker3 Super Moderator Join Date: May 2005 Location: Rural, Oregon GMT -8 Posts: 5,072 Blog Entries: 6

What happened to "then?" Is the "then" supposed to be "Z=1?" Is B a "red herring" variable?

I would contact the instructor to see if there is a typo.
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#3
09-10-2006, 03:03 PM
 rishid New Member Join Date: Oct 2005 Posts: 8

Truth table for this is:
A B C | Z
0 0 0 | 1
0 0 1 | 0
0 1 0 | 1
0 1 1 | 0
1 0 0 | 0
1 0 1 | 1
1 1 0 | 0
1 1 1 | 1

Then I think you just use A,B,C as the select bits in the 8bit mux and draw either 1 or 0's as in puts depedning on the value of Z for the specific mux input
#4
09-10-2006, 03:15 PM
 hgmjr Super Moderator Join Date: Jan 2005 Location: Tennessee, USA (GMT-6) Posts: 9,030 Blog Entries: 11

I think you are going to need to incorporate a 4-input "OR" gate into which you will need to feed the appropriate outputs of the mux to complete the implementation.

hgmjr
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Last edited by hgmjr; 09-10-2006 at 03:19 PM.
#5
09-10-2006, 05:10 PM
 Papabravo Senior Member Join Date: Feb 2006 Location: Michigan, USA (GMT-5) Posts: 5,786

No need for the 4-input gate. The single output of the mux is all you need. The select inputs A, B, and C "select" one of the constant inputs to route to the output. It could hardly be simpler.
#6
09-10-2006, 05:59 PM
 hgmjr Super Moderator Join Date: Jan 2005 Location: Tennessee, USA (GMT-6) Posts: 9,030 Blog Entries: 11

My bad. Papabravo is correct. I was thinking of 3-in / 1-of-8 out decoder when I recommended an OR gate.

hgmjr
__________________
"No human being should be allowed to have this much fun."
hgmjr

May we never lose compassion for those who need our help and encouragement.
#7
09-10-2006, 07:09 PM
 Papabravo Senior Member Join Date: Feb 2006 Location: Michigan, USA (GMT-5) Posts: 5,786

It's an easy mistake to make without a diagram. Although I have known about this technique since I was an undergraduate, I have never had occasion to use it in a career that has spanned nearly four decades.

 Tags 8bit, multiplexer

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