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

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

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

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)): ~0 = 9 ~1 = 8 ~2 = 7 ~3 = 6 ~4 = 5 ~5 = 4 ~6 = 3 ~7 = 2 ~8 = 1 ~9 = 0 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 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) It's too bad universities don't have a money back guarantee. I'd certainly make some noise.

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.

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

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

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