Puzzle #1

Puzzle #1

May 18, 2007

Since I am a big fan of puzzles, I will try to post here from time to time a few digital design related puzzles.

This particular one was given to me in an interview at IBM over 10 years ago.

Due to the war in the land of Logicia there is a shortage of XOR gates. Unfortunately, the only logic gates available are two weird components called “X” and “Y”. The truth table of both components is presented below - Z represents a High-Z value on the output.
Could you help the poor engineers of Logicia to build an XOR gate?

Puzzle #3

Puzzle #3

OK, you seem to like them so here is another puzzle/interview question.

In the diagram below both X and Y are n-bit wide registers. With each clock cycle you could select a bit-wise basic operation between X and Y and load it to either X or Y, while the other register keeps its value.
The problem is to exchange the contents of X and Y. Describe the values of the “select logic op” and “load XnotY” signals for each clock cycle.

Puzzle #10 - Mux Logic

Your company is pretty tight on budget this year and it happens to have only Muxes to design with.
You are required to design a circuit equivalent to the one below, using only Mux structures.