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ALU - Arithmetic and Logical Unit
Interview Questions. Main, FPGA, Digital Fundamentals
ALU: Arithmetic Logical Unit
Most generic computer system is composed of a unit to do arithmetic, logical and shift micro-operations commonly know as ALU. Detailed discussion on computer ALU is discussed below.
ALU is designed to compute arithmetic computations on the binary numbers. The primary format in today’s ALU is two’s complement  (or 2’s complement.). The other possibilities are to use one’s complement or signed-magnitude computations.
Input A
Carry
Control
Flag
Result
Overflow
Input B
ALU Block Diagram
CPU Block Diagram
Fundamental mode of operation of  ALU is dependent on the Control input. The Timing and Control Unit of CPU requests the Aritmetic operations to be performed on Inputs A and B .
PICS
Most common ALU operations are listed below.
Bitwise operations: AND, OR, NOT, XOR here.
Decimal Aritmetic operations - ADD, SUB, MUL and DIV.
Shift Micro-operations.  The output of CPU includes Result of the digital operation, overflow indication and various flags.
The inputs are generally loaded from registers or memory. Similarly, results are also stored into registers or memory. The entire operation of loading the inputs, controlling the operation and storing the results are managed by the external timing and control unit.