# 9's Complement

Discussion in 'Homework Help' started by Muzzleloader, Oct 22, 2007.

Oct 22, 2007
2
0
hello! this is my first post in these forums

and I came here for help with a Digital Logic class

experiment. The problem is:

Design a combinational circuit with four input lines that

represent a decimal digit in BCD and four output lines that

generate the 9's complement of the input digit. Provide a

fifth output that detects an error in the input BCD number.

This output should be equal to logic 1 when the four inputs

have one of the unused combinations of the BCD code.

I need help, my professor has a terrible accent, I can't

ever understand him, and he is an asshole when you ask

him questions. The logic gates you can use are: NAND AND

OR NOR INVERTER and XOR

Thank you, I need an answer asap

2. ### Dave Retired Moderator

Nov 17, 2003
6,960
145
Have you done anything?

My experience of bad tutors suggests that, if what you are saying is correct, you should make a complaint. You, or someone who has an interest, has paid good money for an education and negligent tuition is not acceptable, particularly if it inhibits your ability to a) learn and b) ask questions.

Dave

Oct 22, 2007
2
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it's easy to make suggestions, but the State still wants its percentage of minority Professors. I have paid good money, and its pisses my off....but enough complaining, I have come here for help

I don't have any idea what a 9's complement is and I don't know how to create an error detector. If I knew those things I could at least start

thank you

4. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
The 9's complement of a digit is the number you need to add to it to make that sum equal to 9. Let's use the tilde symbol '~' to mean the 9's complement of.

Code ( (Unknown Language)):
1.
2. ~0 = 9
3. ~1 = 8
4. ~2 = 7
5. ~3 = 6
6. ~4 = 5
7. ~5 = 4
8. ~6 = 3
9. ~7 = 2
10. ~8 = 1
11. ~9 = 0
12.
An error detector in this context is a logic curcuit that outputs a '1' when the four inputs have any of the following six binary patterns:
Code ( (Unknown Language)):
1.
2. 1 0 1 0 = 0xA = 10 (decimal)
3. 1 0 1 1 = 0xB = 11 (decimal)
4. 1 1 0 0 = 0xC = 12 (decimal)
5. 1 1 0 1 = 0xD = 13 (decimal)
6. 1 1 1 0 = 0xE = 14 (decimal)
7. 1 1 1 1 = 0xF = 15 (decimal)
8.
It's too bad universities don't have a money back guarantee. I'd certainly make some noise.

5. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
I suggest having a word with the dean. The professor is being paid to help students with questions, and has an obligation to do so. Part of the dean's responsibility is to make sure the professors live up to theirs.

6. ### techroomt Senior Member

May 19, 2004
198
1
really? i love learning from the wealth of info on this site. i assumed he meant ones complement, or just the complement. thanks papabravo.

Jun 25, 2007
307
1

8. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Think of Binary Coded Decimal.

0000 = 0
0001 = 1
0010 = 2
0011 = 3
0100 = 4
0101 = 5
0110 = 6
0111 = 7
1000 = 8
1001 = 9

Feb 24, 2006
10,340
1,850