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hw8sol

# hw8sol - CSE140 Fall 2006 Homework#8 CSE140 Homework#8...

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CSE140 – Fall 2006 Homework #8 CSE140 Homework #8 - Solutions 5.12 XOR(X,Y) = XY’+X’Y => If X=1 => XOR(X,Y) = Y’ If X=0 => XOR(X,Y) = Y Therefore, XOR gate could be used as a controllable inverter (in this example, the control input is X. If X=1, then the output will be Y’, If X=0, then the output will be Y). The main functionality of the ALU can be broken into four parts: 0, arithmetic, logic, and 1. In order to share one adder for arithmetic commands of ALU, you need to decide when each input must be inverted. The following table is part of the ALU table which deals with arithmetic operations. S2 S1 S0 ALU Operation 0 0 1 Fi=B minus A 0 1 0 Fi=A minus B 0 1 1 Fi=A plus B Based on this table, we can decide for each operation which of the inputs must be inverted. We should also determine the carry which is given to the adder. S2 S1 S0 ALU Operation Adder’s Input1 Adder’s Input2 A’s Inversion B’s Inversion Adder’s Carry In 0 0 1 Fi=B minus A A’ B 1 0 1 (operation is -)

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hw8sol - CSE140 Fall 2006 Homework#8 CSE140 Homework#8...

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