# 74151 Multiplexer

Discussion in 'Homework Help' started by m4yh3m, May 19, 2004.

1. ### m4yh3m Thread Starter Senior Member

Apr 28, 2004
186
42
C|B|A||Y
======
0|0|0||1
0|0|1||0
0|1|0||0
0|1|1||1
1|0|0||0
1|0|1||0
1|1|0||1
1|1|1||1
======

Create a set of input waveforms showing the CBA pattern and apply the proper data bits that will produce output Y

Write the Boolean expression for output Y with respect to the data and select inputs.

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SOMEONE HELP!

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2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Hi

Ah, engineers really like to do it the hard way. By the way, your WN output is actually the compliment of the Y output, or not-Y. We used to indicate it with a bar over the letter, but I can't put it in this text.

The output Y is true when inputs 0, 3, 6 and 7 are selected. That means the other inputs are false. Just assume that the inputs are tied either high or low, and count the A, B and C selection from 0 to 7 to get the outputs.

JerryTam likes this.
3. ### m4yh3m Thread Starter Senior Member

Apr 28, 2004
186
42
Thanks a bunch! Could you possibly tell me how you know that 0, 3, 6, and 7 are the ones needing to be high?

4. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Hi Electricmayhem,

I know because I'm looking at my 1984 Signetics TTL data manual. The 74151 is a multiplexer. The Y output is switched an input depending on the state of the A, B and C selection bits.

Look at the truth table for the states of the selection bits when Y is true. I'm assuming that A is bit 0, and C is bit 2 here. Since Y has to follow the selected input as the bits count from 0 to 7, then it follows that inputs 0, 3, 6 & 7 are high, and the others low.

It may help that I've been doing this stuff for 37 years, too. I was trained as a technician, so I look at problems/designs from a different angle.

JerryTam likes this.