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Apr2-12, 12:39 PM
Sci Advisor
HW Helper
P: 7,292
Quote Quote by Femme_physics View Post
According to the data the decoder acts on low. So telling me that the decoder has no need for choice signal - CS, seems like an irrelevant bit of information to solve for which code let's out which exit. I mean, it doesn't change the truth table right?
It does change the truth table. If CS is "off", you get no output at all, for ANY values of the the other inputs.

For your problem, you probably aren't interested in using that behaviour, so you can ignore it in your truth tables. But if you build or simulate the circuit, you have to connect the CS pin permanently to the right input voltage, otherwise nothing will work.