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4 problems, 5 pages Exam Two 22 March 2000
Instructions: This is a closed book, closed note exam. Calculators are not permitted. If you have a question, raise your hand and I will come to you. If you finish early, please check your work until the bell rings so as not to disturb others that are still working. Please work the exam in pencil and do not separate the pages of the exam. For maximum credit, show your work. Good Luck!
Your Name ( please print ) ________________________________________________
1 2 3 4 total
4 problems, 5 pages Exam Two 22 March 2000
Problem 1 (3 parts, 30 points) Implementing Storage
For each part of this problem, connect the inputs and output of your design to the named signals.
Part A (10 points) Using only the devices below, implement a two-to-one mux.
Part B (10 points) Now using this two-to-one mux, implement a transparent latch using basic gates (NAND, NOR, AND, OR, NOT, pass). Try to minimize transistors.
Part C (10 points) Now using a two-to-one mux and two transparent latches, implement a register with read and write enable using basic gates (NAND, NOR, AND, OR, NOT, pass).
4 problems, 5 pages Exam Two 22 March 2000
Problem 3 (2 parts, 20 points) State Machine
Part A (15 points) Complete the state table for the following state machine. Recall that in a state diagram, an arc annotation “M/N” suggests input M is high and output N is high; all other inputs and outputs are low. A is an input; X is an output; S is the current state; NS is the new state.
S 1 S 0 A NS 1 NS 0 X S 1 S 0 A NS 1 NS 0 X
Part B (5 points) The primary output of this state machine is S 1 and S 0. What is its function?
4 problems, 5 pages Exam Two 22 March 2000
Problem 4 (2 parts, 20 points) Priority Fun
Consider a priority encoder with the following behavior:
In3 In2 In 1
In 0 O 1 O 0 Valid
0 0 0 0 X X 0
X 0 0 1 0 0 1
X X 1 X 0 1 1
X 1 0 X 1 0 1
Part A (10 points) List the inputs (In 0 , In 1 , In 2 , and In 3 ) in increasing priority.
lowest priority 3 rd^ highest priority 2 nd^ highest priority highest priority
Part B (10 points) The behavior of O 1 is summarized below (in map format). Derive a simplified sum of products expression using a Karnaugh Map. Circle and list the prime implicants, indicating which are essential. Then write the simplified SOP expression.
O 1 =
