Re: Please Help me Somebody with DEMUX Gate

Posted by WBahn on May 21, 2019; 10:10pm
URL: http://nand2tetris-questions-and-answers-forum.52.s1.nabble.com/Please-Help-me-Somebody-with-DEMUX-Gate-tp4033175p4033190.html

I think the problem is that you are looking for ready-made solutions on the Internet instead of designing circuit to solve the problem yourself -- and that's what N2T is all about.

Do you understand either of those two circuits and HOW they work so as to achieve the desired functionality? Do you even know what each of the inputs is on the right-hand circuit?

If so, then seeing how to combine them to make a multi-bit gate is quite apparent. But if not, then it would be very difficult to see how to so.

Let's focus on how to DESIGN the circuit, now how to find it on some website someplace.

You want a 1:2 DeMux in which the input is echoed to exactly one of the outputs with all other outputs being LO. Which output receives the input is determined by the select input.

Let's say that our input is called 'in' and the select input is called 'sel'. Our outputs are 'a' and 'b'. Note that these match the authors' signal names, I prefer out0 and out1 myself.

If 'sel' = 0, the the input is echoed to output 'a', otherwise it is echoed to output 'b'.

Since you have two outputs, you have two truth tables. What are the truth tables for each output in terms of the 'in' signal and the 'sel' signal?