I'm stuck in this problem, Can somebody help me? Imagine a machine with four inputs and one output that functions as follows: the output is ON if exactly two of the inputs are one, and off otherwise. Draw a circuit that performs this function. Use a truth table to show that all possible input values produce the proper output. Thanks..
If you draw out the truth table, you'll find there are 6 possible combinations of "winning" inputs. Assuming the inputs are labelled A, B, C, D, the combinations are: A.B A.C A.D B.C B.D C.D If you're only allowed to use 2-input gates, then first of all use 6 2-input AND gates to give these outputs. Now, we're only interested in a positive output if one and ONLY one of these combinations exists, so we need a sequence of XOR gates. Again, if we're only allowed 2-input XOR gates, you'll need 5 of them to whittle the 6 outputs down to 1. This should solve your problem...hope it helps!! Scarydave
Truth Table A B C D X 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 1 1 1 0 1 0 0 0 0 1 0 1 1 0 1 1 0 1 0 1 1 1 1 1 0 0 0 0 1 0 0 1 1 1 0 1 0 1 1 0 1 1 1 1 1 0 0 1 1 1 0 1 1 1 1 1 0 1 1 1 1 1 1
The function is true if 2 and only 2 inputs are true. A B C D X 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 1 1 1 0 1 0 0 0 0 1 0 1 1 0 1 1 0 1 0 1 1 1 0 1 0 0 0 0 1 0 0 1 1 1 0 1 0 1 1 0 1 1 0 1 1 0 0 1 1 1 0 1 0 1 1 1 0 0 1 1 1 1 0
Ron is correct. The problem does not even specify gates - only "circuit." The solution may be implimented with only a 74154 and a 7411.