prelim1-20fa

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Cornell University *

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3410

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Computer Science

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Jan 9, 2024

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Fall 2020 Prelim 1 CS 3410, Cornell University Please turn off and stow away all electronic devices including smart watches. You may not use them for any reason during the exam. Do not bring them with you if you leave the room temporarily. This is a closed book and notes examination. You may use the 4-sided reference sheet provided. There are 9 problems . Make sure you have the whole exam. You have 90 minutes to complete 90 points. Use your time accordingly. Question Points Score 1 4 2 6 3 9 4 18 5 10 6 6 7 5 8 12 9 20 Total: 90 It is a violation of the Academic Integrity Code to look at any exam other than your own, to look at any other reference material, or to otherwise give or receive unauthorized help. We also ask that you not discuss the exam with anyone who has not yet taken it. Academic Integrity is expected of all students of Cornell University at all times, whether in the presence or absence of members of the faculty. Understanding this, I declare I shall not give, use or receive unauthorized aid in this examination. Signature: Date Name: NetID
1. [4 points] “On the king’s gate the CMOS grew gray.” —Helen Hunt Jackson (sort of) Recall that a p-transistor connects source to drain when a negative/zero charge is applied to the gate. What function does the following CMOS diagram implement? (Hint: truth table!) Your Answer: A B OUT ground Vdd “hop over” means wires do not connect 2. “I know numbers are beautiful. If they aren’t beautiful, nothing is.” —Paul Erdos (a) [2 points] Express the unsigned integer 11001010 in decimal (base 10). Your Answer: (b) [2 points] Express the 2s complement number 011001010 in octal (base 8). Your Answer: (c) [2 points] Express the decimal (base 10) number -48 in a 16-bit 2’s complement number. Make sure your answer is 16 bits long. Your Answer: Page 2
3. De secret’s in de mux . A multiplexer , or mux , takes multiple inputs and—based on a control input—and selects one of the inputs to be the output. The converse of the multiplexer is the demultiplexer (or demux ). Also called a data distrib- utor, a demultiplexor is an important component in networking. A 1:4 demux takes a single input ( D ) and routes it to one of several outputs ( Y 0 - Y 3 ) based on the 2-bit select input S 1 S 0 . The non-selected outputs remain 0. (a) [4 points] Complete the truth table for a 1-bit 1:4 demux. (Use the diagram on the left to disambiguate which select signal is associated with which output.) 00 01 10 11 Y 0 Y 1 Y 2 Y 3 S 0 S 1 D 1-bit 1:4 Demux Example Input/Ouputs: D = 1 S = 10 O = 0 1 00 1 0 0 0 1 0 S 1 S 0 D Y 0 Y 1 Y 2 Y 3 0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1 (b) [5 points] Using only basic 1- and 2-input logic gates (see reference sheet), draw the gate- level implementation of a 1-bit 1:2 demux . Label all inputs and outputs using the names/conventions shown above. Page 3
4. Register to vote! This is the 32-bit, 32 register, dual-read and single-write register file presented in lecture: (a) [5 points] We want the register file to have 64-bit registers instead of 32-bit registers . Which signals need to be modified/replicated/removed to support the new register file? Circle all that apply: A B C D E F G None Which components need to be modified/replicated/removed to support the new register file? Circle all that apply: W X Y Z None (b) [5 points] We want the register file to be dual-write instead of single-write . Which signals need to be modified/replicated/removed to support the new register file? Circle all that apply: A B C D E F G None Which components need to be modified/replicated/removed to support the new register file? Circle all that apply: W X Y Z None Page 4
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