Mon, 5 Sep 2011, 22:10

I guess Labor Day weekend is now really over!  Another student writes:

> I had a question about number 2. The description says that each box can
> either add or multiply two inputs and output their sum or product. However,
> can you use the output from one box multiple times? In other words, can you
> just assume we wanted to run the add or multiply operation twice. For
> instance, if an add box outputs (y+z) and you wanted to use another (y+z) to
> make (y+z)^2 with a multiply box, could you just make (y+z) the other input?
> Sorry about the confusing description. 
> 
> <<name withheld to protect the student who is sorry about the description>>

The short answer: Absolutely!  In fact, this is very common in computer
logic circuit design - we implement a function and then use its output as
input in more than one place.  In fact, we have a name for such: it is called
fan-out.  For electrical reasons (and electrical reasons are beyond what I
want to do in EE 306 - we will save that for 316), we usually restrict the
output of any "box" from being used as an input to more than four other boxes.
That is, most logic circuits have a maximum fan-out of 4.

Good luck with the rest of the problem set.  See you in class on Wednesday.

Yale Patt