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#1
10-22-2007, 10:28 PM
 Muzzleloader New Member Join Date: Oct 2007 Posts: 2
9's Complement

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
10-22-2007, 10:46 PM
 Dave Senior Member Join Date: Nov 2003 Posts: 6,961 Blog Entries: 17

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
#3
10-22-2007, 11:49 PM
 Muzzleloader New Member Join Date: Oct 2007 Posts: 2

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
10-23-2007, 12:26 AM
 Papabravo Senior Member Join Date: Feb 2006 Location: Michigan, USA (GMT-5) Posts: 5,831

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:
```~0 = 9
~1 = 8
~2 = 7
~3 = 6
~4 = 5
~5 = 4
~6 = 3
~7 = 2
~8 = 1
~9 = 0```
Select All
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:
```1 0 1 0 = 0xA = 10 (decimal)
1 0 1 1 = 0xB = 11 (decimal)
1 1 0 0 = 0xC = 12 (decimal)
1 1 0 1 = 0xD = 13 (decimal)
1 1 1 0 = 0xE = 14 (decimal)
1 1 1 1 = 0xF = 15 (decimal)```
Select All
It's too bad universities don't have a money back guarantee. I'd certainly make some noise.
__________________
We never have time to do it right,
But we always have time to do it over.
#5
10-23-2007, 02:52 AM
 thingmaker3 Super Moderator Join Date: May 2005 Location: Rural, Oregon GMT -8 Posts: 5,072 Blog Entries: 6

Quote:
 Originally Posted by Muzzleloader and he is an asshole when you ask him questions.
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.
__________________
"I want to establish in your mind very clearly that you must not think I deny all that I do not admit. On the contrary, I think there are many things which may be true, and which I shall receive as such hereafter, though I do not as yet receive them; but that is not because there is any proof to the contrary, but that the proof in the affirmative is not yet sufficient for me"
#6
10-23-2007, 03:35 PM
 techroomt Senior Member Join Date: May 2004 Location: pennsylvania Posts: 198

Quote:
 The 9's complement of a digit is the number you need to add to it to make that sum equal to 9
really? i love learning from the wealth of info on this site. i assumed he meant ones complement, or just the complement. thanks papabravo.
#7
10-23-2007, 11:57 PM
 arthur92710 Senior Member Join Date: Jun 2007 Location: NY, USA Posts: 307

[QUOTE=Papabravo;43564]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:
```~0 = 9
~1 = 8
~2 = 7
~3 = 6
~4 = 5
~5 = 4
~6 = 3
~7 = 2
~8 = 1
~9 = 0```
Select All
Well... after your explanation It sounds easy.
I never herd of it.
But binary doesn't go to 9 only 2 (0 and 1)
Would it be like...
0000 = 1001
0001= 1000
0010= 0111
...ect...
#8
10-24-2007, 01:01 AM
 beenthere Senior Member Join Date: Apr 2004 Location: Missouri, USA (GMT -6) Posts: 15,815 Blog Entries: 10

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
#9
10-24-2007, 10:19 AM
 Papabravo Senior Member Join Date: Feb 2006 Location: Michigan, USA (GMT-5) Posts: 5,831

So to take the tens complement of a number you can take the 9's complement and add one. Think about representing negative numbers in tens complement notation.

http://en.wikipedia.org/wiki/Method_of_complements
__________________
We never have time to do it right,
But we always have time to do it over.

Last edited by Papabravo; 10-24-2007 at 10:24 AM.

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