exam2a_sol

# If there are 225 opcodes and 120 registers a what is

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If there are 225 opcodes and 120 registers: a) What is the minimum number of bits required to represent the OPCODE? 8 bits b) What is the minimum number of bits required to represent the destination register DR, and source registers SR1 and SR2? (Give the total number of bits.) 7 * 3 = 21 bits c) What is the maximum number of UNUSED bits in the instruction encoding? 32 – 21 – 8 = 3 bits

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4 Problem 3 (3 points) The figure below shows a combinational logic circuit. Complete the truth table corresponding to this circuit. Inputs Output A B C Z 0 0 0 1 0 0 1 0 0 1 0 1 0 1 1 0 1 0 0 0 1 0 1 0 1 1 0 1 1 1 1 1
5 Problem 4 (2 points) You know a byte is 8 bits. A 4-bit quantity is called a nibble . If a byte-addressable memory has a 16-bit address, how many nibbles of storage are in this memory? 2 16 * 8/4 = 2 17 = 131072 nibbles Problem 5 (3 points) The circuit below has a major flaw. Can you identify it? Hint : Evaluate the circuit for all sets of inputs. There is short circuit (path from Power to Ground) when either A = 1 and B = 0 or A = 0 and B = 1.

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6 Problem 6 (4 points) Fill in the truth table for the following transistor level circuit. Note that two wires with the same name are assumed to be connected to each other.

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