# Need Urgent help logic circuits

#### WBahn

Joined Mar 31, 2012
26,398
Anyone know why colleges seem to want to teach excess-3 codes so often? I know why they were important in the fifties and sixties, but there's really no need now. I think it would be more important to teach ASCII, maybe EBCDIC, and newer expanded character codes. Maybe that comes later.
Excess-N is simply a means of representing negative integers in a fixed-width weighted binary system. It is taught both because it is one of several ways of representing negative integers and is therefore useful in introducing and discussing the pros and cons of such representations and also because it is very widely used -- anyone that uses floating point variables (that use IEEE-754 representation) since that is how the exponent is represented.

The use of excess-3 is common not so much because of the historical advantages it has in a BCD system, but rather because it is something that is very easy for students to understand and to work with on paper. Any excess-N representation with N < 7 can represent the positive digits. For the basics I tend to use a 3-bit representation using either excess-3 or excess-4 in part because 3-bits doesn't take as much time to enumerate on the board and also because I want to divorce the conversation from any kind of BCD notions, which students have a very hard time doing.

#### Kermit2

Joined Feb 5, 2010
4,162
If your friend is willing to let you have his answer to the question, why can you not get HIM to guide you through it and explain the steps? He is letting you use his answer, so he would be the logical choice to explain his answer.

#### dl324

Joined Mar 30, 2015
13,142
He is letting you use his answer, so he would be the logical choice to explain his answer.
Both of the examples posted are wrong...

#### djsfantasi

Joined Apr 11, 2010
7,842
Both of the examples posted are wrong...
But discussing it with his friend may result in both seeing the error and correcting it. Collaboration!

#### dl324

Joined Mar 30, 2015
13,142
But discussing it with his friend may result in both seeing the error and correcting it. Collaboration!
True. My experience in college was that people asking for help really just wanted to copy your answer.

#### djsfantasi

Joined Apr 11, 2010
7,842
<hijack>
True. My experience in college was that people asking for help really just wanted to copy your answer.
My experience was different. We formed independent study groups. I was good at abstractly applying the theory (we know this and then that and this other thing lets us prove X) and my buddy was good with the details ('this' would be Theorem 10.2, pp.110-112, 'that' would be Theorem 11.5... etc).

</hijack>