Practice Problems, 1/23/03

Practice Problem 1: How to build the whole world out of NOR gates

a. Build an inverter using a NOR gate

b. Using the inverter from (a), and a NOR gate, build an OR gate

c. Using two inverters and the OR gate from (b), build a NAND gate

d. Using the NAND gate from (c) and an inverter, build an AND gate

e. Using two inverters, two ANDs, and an OR, build an XOR gate

Practice Problem 2:

a. Consider the R-S latch that we looked at in class. Now, suppose that both the R and S lines go to 1. What happens to the lines X and Q?

b. Suppose that we continue from this situation by bringing the R line back to 0. Now what happens to the lines X and Q?

c. Continuing on from b, now what happens if we bring S back to 0?

d. Is there any situation in which the R-S latch could truly get confused (i.e., in which there would be no consistent assignment for the X and Q lines)?