Computer architecture

COMPUTER COMPUTER ARCHITECTUREARCHITECTURE

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NITU SRIVASATAVA NITU SRIVASATAVA

BINARY ADDERBINARY ADDERThe digital circuit that The digital circuit that

generates the arithmetic sum generates the arithmetic sum of two binary numbers of any of two binary numbers of any

length is called a BINARY length is called a BINARY ADDER.ADDER.

CONSTRUCTIONCONSTRUCTION

The binary adder is constructed with full- The binary adder is constructed with full- adder circuits connected in cascade, with adder circuits connected in cascade, with the output carry from one full-adder the output carry from one full-adder connected to the input carry of the next connected to the input carry of the next full-adder.full-adder.

An n-bit binary adder requires ‘n’ full-An n-bit binary adder requires ‘n’ full-adders.adders.

The n data bits for the inputs A and B The n data bits for the inputs A and B comes from registers (such as R1 and R2). comes from registers (such as R1 and R2).

4-BIT BINARY ADDER4-BIT BINARY ADDER

BINARY ADDER-SUBTRACTORBINARY ADDER-SUBTRACTOR

The addition and subtraction The addition and subtraction operations can be combined into one operations can be combined into one common circuit called BINARY common circuit called BINARY ADDER-SUBTRACTOR.ADDER-SUBTRACTOR.

This can be done by including an This can be done by including an exclusive-OR gate with each full exclusive-OR gate with each full adder in binary adder.adder in binary adder.

4-BIT BINARY ADDER-4-BIT BINARY ADDER-SUBTRACTORSUBTRACTOR

WORKINGWORKING

Each exclusive-OR gate receives input M Each exclusive-OR gate receives input M and one of the inputs of B.and one of the inputs of B.

The mode input M controls the operation.The mode input M controls the operation. When M=0,we have B(+)0=B.The full- When M=0,we have B(+)0=B.The full-

adders receives the value of b,the input adders receives the value of b,the input carry is 0,the circuit performs A+B.carry is 0,the circuit performs A+B.

When M=1,we have B(+)1=B’ and When M=1,we have B(+)1=B’ and Carry=1.The B inputs are complemented Carry=1.The B inputs are complemented and a 1 is added through the input and a 1 is added through the input carry.The circuit performs the operation A carry.The circuit performs the operation A plus the 2’s complement of B. plus the 2’s complement of B.

4-BIT BINARY INCREMENTER

BINARY INCREMENTERBINARY INCREMENTER

The increment microoperation adds The increment microoperation adds one to a number in a register.one to a number in a register.

This increment can be done This increment can be done independent of a register by the independent of a register by the means of a combinational circuit means of a combinational circuit called BINARY INCREMENTER.called BINARY INCREMENTER.

ARITHMETIC CIRCUITARITHMETIC CIRCUIT

All the arithmetic microoperations All the arithmetic microoperations can be implemented in one can be implemented in one composite arithmetic circuitcomposite arithmetic circuit

The basic component of an The basic component of an arithmetic circuit is the parallel arithmetic circuit is the parallel adder.adder.

By controlling the data inputs to the By controlling the data inputs to the adder,it is possible to obtain different adder,it is possible to obtain different types of arithmetic operations.types of arithmetic operations.

4-BIT ARITHMETIC CIRCUIT4-BIT ARITHMETIC CIRCUIT

It has 4 full adder circuits that It has 4 full adder circuits that constitute the 4-bit adder and four constitute the 4-bit adder and four multiplexers for choosing different multiplexers for choosing different operations.operations.

There are two 4-bit inputs A and B There are two 4-bit inputs A and B and a 4-bit outout D.and a 4-bit outout D.

The 4 multiplexers are controlled by The 4 multiplexers are controlled by two selection inputs,So and S1.two selection inputs,So and S1.

4-BIT ARITHMETIC CIRCUIT4-BIT ARITHMETIC CIRCUIT