2-function output - Decoder to NAND gate

Discussion in 'Homework Help' started by Jason Ramirez, Sep 29, 2014.

1. Jason Ramirez Thread Starter New Member

Sep 29, 2014
1
0
Hello everyone, new to this forum and looking for some tips to put me in the right direction. Please don't give me a full solution as I like the problem solving aspect, but am a little stuck.

We are given 2 functions:

X=/A/B/CD+/A/BCD+ABCD+ABC
Y=AB/CD+BCD+/A/CD+ABD

from that, I got:
X=E(1,3,14,15)
Y=E(1,5,7,13,15)

From here, I need to:
"Show input connections necessary to realize the above Boolean expressions using exactly two 3-to-8 Decoders (2 of 74138 chips) and two 4-input NAND gates (7420 chip). No other gates allowed."

I understand how to combine the 2 decoders to create a 4-to-16 decoder, using A as an input to G2A and/or G2B on one chip and to the G1 with G2A/G2B set to ground/low on the other. What I dodn't understand is the part of only having 2 4-input NAND gates to process the decoder outputs to create the X and Y functions.

Even using DeMorgan, I get:
/(/A/B/CD)+/(/A/BCD)+/(ABCD)+/(ABC)
for X, and y has 5 outputs.

I assume there is a concept I should be applying that maybe I need to research (perhaps I missed it or will be learning it in next class, which I will be missing). So if that is the issue, a concept I need to used, please let me know that so I can look up info on that and learn it.

Thank you again for all help anyone can provide.