EE 2301
Introduction to Digital Systems Design
Fall 2020
Midterm 1
Thurs., Oct. 23, 2020, 9:45AM to 11:00AM.
1. Number Systems and the Complement Method for Negative Numbers [25 points]
(a) Number Systems
Consider this expression
WTF36 + CWOT36
What is the result, in base 36? [5 points] (b) Complement Method
In class,we learned how to compute the two’s complement of a number in base 2. Consider now a generalization of that concept to other bases. Consider base b. With n digits, represent the negative of a number v as bn − v. (Call this “b’s complement.”)
i. For base 11, what range of numbers can you represent with 2 digits? Express your answer in decimal. [5 points]
ii. Show how to perform. the operation 5A11 − 1A11 in 11’s complement arith- metic:
• First show how to represent −1A11 in the complement system.
• Then add that result to 5A11, discarding the overflow, if any.
• Confirm that the result is correct (by show the subtraction in base 10). [15 points]
2. Truth Tables, Boolean Expressions, and Gates [25 points] Consider a function f(W,X,Y, Z) that is one if W = X and Y Z
(a) Fill in the following truth table. [5 points] inputs
(b) Write a minimal OR-AND two-level expression for this function. [10 points]
(c) Write a minimal NOR-NOR two-level expression for this function. [5 points]
(d) Write an XNF expression for this function, that is, an expression consisting of the XOR of AND terms, with no negations. [10 points]
3. Circuits for XOR [25 points]
Draw a circuit to compute the XOR function of 15 variables with only AND gates, OR gates, and inverters. Use as few AND gates as and OR gates possible. (Note that you can define smaller circuits, put these in “boxes”, and use these boxes to build larger circuits. However, you must specify everything in the smallest box.)
4. Circuits with Feedback [25 points]
Consider the following circuit:
What are the outputs f1 and f2 for the following input combinations?
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