CPSC 5155 Introduction to Computer Architecture
Mid-Term Exam Thursday, February 22, 2007
THIS TEST IS OPEN-BOOK, OPEN-NOTES.
DO NOT PUT ANY ANSWERS ON THIS PAPER. GOOD LUCK!
1. (20 points) The following diagram is a modified SR flip–flop. Use a truth table and the
characteristic table of an SR flip–flop to determine its characteristic table for inputs X and Y.
2. (20 points) Evaluate the following Boolean expressions, assuming that
A = 0, B = 1, C = 0, and D = 1 (1 = logical TRUE, 0 = logical FALSE).
a) F(A, B) = A
B
+
A
B
b) F(A, B, C, D) = A
B
+
C
D + CD
c) F(A, B, C, D) =
A
B(A +
B
+
C
D) +
B
D
3. (20 points) What does the following circuit do? Describe it using a truth table.
Remember that this circuit has four NAND gates, which are AND followed by a NOT.
4. (20 points) Consider the Boolean function of three Boolean variables A, B, and C
described by the POS expression F(A, B, C) = (1, 3, 6, 7).
Implement this function using a decoder of appropriate size.
5. (20 points) A computer memory system uses a primary memory with 100 nanosecond
access time, fronted by a cache memory with 8 nanosecond access time. What is the
effective access time if
a) The hit ratio is 0.8?
b) The hit ratio is 0.9?
c) The hit ratio is 0.98?