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!

 

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.

 

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

 

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.