prepared by: Sanchita mishra Sonkali bhalavi sunita Submitted to: Shweta agrawal

Design of arithmetic logical unit(alu)

An Arithmetic logic unit(ALU) Is a digital circuit used to perform Arithmetic & logical unit.For example Add,sub,multiplication,etc

An ALU can be divided into two segments- the arithmetic unit & logical unit. The arithmetic unit performs typical operation such as addition,subtraction, and increment, decrement by 1.usually, operands involved may be signed or unsigned interges.however,an arithemetic unit must handle 4-bit bcd numbers & floating-point numbers ARITHMETIC UNIT

AS NAME IMPLIES, THE LOGIC UNIT CONTAIN HARDWARE ELEMENT THAT PERFORM TYPICAL OPERATION SUCH AS BOOLEAN NOT & OR. HERE, THE DESIGN OF A SIMPLE ALU USING TYPICAL COMBINATIONAL ELEMENT SUCH AS GATE,MULTIPLEXERS, AND 4-BIT PARALLEL ADDER IS DISCUSSED. FOR THIS APPROACH, FIRST AN ARITHMETICAL UNIT AND LOGICAL UNIT ARE DESIGNED SEPERATELY, THEN THEY ARE COMBINED TO OBTAIN AN ALU…………………

 Most of a processor's operations are performed by one or more ALU. An ALU loads data from input registers, executes, and stores the result into an output register. A Control Unit tells the ALU what operation to perform on the data. Other mechanisms move data between these registers and memory. Pratical overview

, as this is the representation that makes it easier for the ALUAn ALU must process numbers using the same format as the rest of the digital circuit. For modern processors, that almost always is the two's complement binary number representation. Early computers used a wide variety of number systems, including one's complement, sign-magnitude format, and even true decimal systems, with ten tubes per digit.  ALUs for each one of these numeric systems had different designs, and that influenced the current preference for two's complements to calculate additions and subtractions. Numerical ststem

 Most ALUs can perform the following operations: 1. Integer arithmetic operations (addition, subtraction, and sometimes multiplication and division, though this is more expensive) 2. Bitwise logic operations (AND, NOT, OR, XOR) 3. Bit-shifting operations (shifting or rotating a word by a specified number of bits to the left or right, with or without sign extension). Shifts can be interpreted as multiplications by 2 and divisions by 2. Simple operation

 An engineer can design an ALU to calculate any operation, however it is complicated; the problem is that the more complex the operation, the more expensive the ALU is, the more space it uses in the processor, and the more power it dissipates, etc.  Therefore, engineers always calculate a compromise, to provide for the processor (or other circuits) an ALU powerful enough to make the processor fast, but yet not so complex as to become prohibitive. Complex operation

The logical operations are easiest, because they map directly onto the hardware components. The 1-bit logical unit for AND and OR looks like figure below. The multiplexor on the right then selects a AND b or a OR b, depending on whether the value of Operation is 0 or 1. The line that controls the multiplexor is shown in color to distinguish it from the lines containing data. In the figure below control and output lines of the multiplexor were renamed to names that reflect the function of the ALU. A 1-BIT ALU