ALU Description

Inputs:

$-$ Data A $(4-$bits$)$

$-$ Data B $(4-$bits$)$

$-$ Mode $(1-$bit$)$

$-$ Selection $(2-$bits$)$

Outputs:

$-$ Operation Results F $(4-$bits$)$

$-$ Comparator Results $(3-$bits$)$

$-$ Carry Out $(2-$bits$)-$ One bit for Addition operation and one bit for Subtraction operation

Description of ALU Controls: Mode $($M$)$ and Selection $(\backslash (\backslash$mathrm$\{$S$\}\_\{1\}\backslash$mathrm$\{$~S$\}\_\{0\}\backslash ))$:

$-$ Depending on the mode and selection the ALU will perform a specific operation. Mode $0$ will perform arithmetic operation while model $1$ will perform logic operations. The selection inputs will determine the specific operation in each mode. See table below for details on each operation.

The best approach to design the ALU is to take a modular approach. That is$,$ design, build and test each component first. The following steps will assist you in designing the complete ALU:

$-$ Design a $2$ Channel $4-$bit MUX

$-$ Design a $4$ Channel $4-$bit MUX

$-$ Design the Logic unit. $($See Figure $2)$

$1.$ Design a subcircuit that takes two $4-$bit inputs $($A$,$ B$)$ and performs a bitwise AND operation

$2.$ Design a subcircuit that takes two $4-$bit inputs $($A$,$ B$)$ and performs a bitwise OR operation

$3.$ Design a subcircuit that takes two $4-$bit inputs $($A$,$ B$)$ and performs a bitwise XOR operation

$4.$ Design a subcircuit that takes one $4-$bit input $($A$)$ and performs bitwise Inverse operation

$5.$ Use a MUX to combine all four subcircuits to create the logic unit