You need a 3x8 decoder. Unfortunately, when you go to the hardware store, they only have 2x4 ones. So you decide to buy two 2x4 decoders, plus some gates (precisely, two chips of 4 AND each, and one chip of 4 inverters). Using these, design a 3x8 decoder.

 

And what have you done so far with your chips? Do you have a first try schematic? If we are o help, we need to know where you are stuck. Otherwise, no one will respond because this is Homework HELP, and we don't do it for you.

 

And what have you done so far with your chips? Do you have a first try schematic? If we are o help, we need to know where you are stuck. Otherwise, no one will respond because this is Homework HELP, and we don't do it for you.

 

And what have you done so far with your chips? Do you have a first try schematic? If we are o help, we need to know where you are stuck. Otherwise, no one will respond because this is Homework HELP, and we don't do it for you.

 

This is how real-world 2x4 decoders look like...


So does it help?

 

Unless I'm thinking about this wrong, with 8 AND gates and 1 NOT gate, you only need 1 2x4 decoder -- and you don't need a decoder that has an enable input. If you have two 2x4 decoders with an enable input, then you only need a single NOT gate to make a 3x8 decoder.

Make an effort -- don't just say that you are confused, throw your hands up, and expect someone else to show you how to do it.

 

So, now you have how a real 2x4 decoder looks like. Do you know how they work and if not, how to find out for yourself (hint: datasheet)?

 

How a "real" decoder works may not be relevant -- many intro logic classes work with basic blocks that do not include output enables, which is what the TS is showing in the little bit of "work" they have shown thus far. So if what he shows is the building block he has available, then it is what it is.

 

WBahn is right.

You just need 8 AND gates and an inverter and a 2x4 decoder without EN input. I just sim it on proteus and it works. Didn't realize it at first glance.

But are there really any 2x4 decoder without "Enable" in the hardware store?

You need a 3x8 decoder. Unfortunately, when you go to the hardware store, they only have 2x4 ones.

Allen