This document provides an overview of the topics covered in Session 3 of the CS307PC course on Computer Organization and Architecture. The session covered Register Transfer Language and microoperations, including register transfer, bus and memory transfers, and different types of microoperations such as arithmetic, logic, and shift microoperations. It provides examples of arithmetic microoperations like addition and subtraction. Binary adders and incrementers are discussed as implementations of arithmetic microoperations. The next session will cover logic and shift microoperations as well as arithmetic shift logic units.

1. CS307PC:Computer Organization
and Architecture (R18 II(I sem))
Department of computer science and engineering
(AI/ML)
Session 3
by
Asst.Prof.M.Gokilavani
VITS
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2. TEXT BOOK:
• 1. Computer System Architecture – M. Moris Mano, Third Edition,
Pearson/PHI.
REFERENCES:
• Computer Organization – Car Hamacher, Zvonks Vranesic, Safea
Zaky, Vth Edition, McGraw Hill.
• Computer Organization and Architecture – William Stallings Sixth
Edition, Pearson/PHI.
• Structured Computer Organization – Andrew S. Tanenbaum, 4th
Edition, PHI/Pearson.
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3. UNIT - I
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Digital Computers: Introduction, Block diagram of Digital Computer,
Definition of Computer Organization, Computer Design and Computer
Architecture.
Register Transfer Language and Micro operations: Register Transfer
language, Register Transfer, Bus and memory transfers, Arithmetic
Micro operations, logic micro operations, shift micro operations,
Arithmetic logic shift unit.
Basic Computer Organization and Design: Instruction codes,
Computer Registers Computer instructions, Timing and Control,
Instruction cycle, Memory Reference Instructions, Input – Output and
Interrupt.

4. Topics covered in session 3
• Register Transfer Language and Micro operations
• Register Transfer language
• Register Transfer
• Bus and memory transfers
• Arithmetic Micro operations
• logic micro operations
• shift micro operations
• Arithmetic logic shift unit
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5. Micro operations
• The operations performed on the data stored in registers are called micro
operations.
• A micro operation is an elementary operation performed on the data stored in one
or more registers.
• Computer system micro operations are of four types:
1.Register transfer micro-operations transfer binary information from one register to
another.
2.Arithmetic micro-operations perform arithmetic operations on numeric data stored
in registers.
3.Logic micro-operations perform bit manipulation operation on non-numeric data
stored in registers.
4.Shift micro-operations perform shift micro-operations performed on data.
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6. Arithmetic Micro-operation
• Arithmetic micro operations perform arithmetic operations on numeric
data stored in registers.
• The basic arithmetic micro operations are
• Addition, Addition with carry
• Subtraction, subtraction with borrow
• Increment/Decrement
• Shift.
Example:
Assume that th input data are in register R1, 𝑅2 is th symbol for 1’s
complement of R2. Adding 1 to th 1’s complement produces the 2’s
complement. Adding th contents of R1 to the 2’s complement of R2 is
equivalent to R1-R2.
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7. Arithmetic Micro-operation
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• Arithmetic shift are explained later in conjunction with the shift micro operations.
The arithmetic micro operation defined by the statement:

8. Binary Adder
• The Add micro-operation requires registers that can hold the data and the
digital components that can perform the arithmetic addition.
• A Binary Adder is a digital circuit that performs the arithmetic sum of two
binary numbers provided with any length.
• A Binary Adder is constructed using full-adder circuits connected in series,
with the output carry from one full-adder connected to the input carry of the
next full-adder.
• The augend bits (A) and the addend bits (B) are designated by subscript
numbers from right to left, with subscript '0' denoting the low-order bit.
• The carry inputs starts from C0 to C3 connected in a chain through the full-
adders. C4 is the resultant output carry generated by the last full-adder
circuit.
• The output carry from each full-adder is connected to the input carry of the
next-high-order full-adder.
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9. Binary Adder
• The following block diagram shows the interconnections of four full-adder circuits to provide a 4-bit
binary adder.
• The sum outputs (S0 to S3) generates the required arithmetic sum of augend and addend bits.
• The n data bits for the A and B inputs come from different source registers. For instance, data bits
for A input comes from source register R1 and data bits for B input comes from source register R2.
• The arithmetic sum of the data inputs of A and B can be transferred to a third register or to one of the
source registers (R1 or R2).
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10. Binary Adder - Subtractor
• The Subtraction micro-operation can be done easily by taking the 2's compliment of
addend bits and adding it to the augend bits.
• The Arithmetic micro-operations like addition and subtraction can be combined into one
common circuit by including an exclusive-OR gate with each full adder.
• The block diagram for a 4-bit adder- Subtractor circuit can be represented as:
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11. Binary Adder - Subtractor
• When the mode input (M) is at a low logic, i.e. '0', the circuit act as an adder and
when the mode input is at a high logic, i.e. '1', the circuit act as a subtractor.
• The exclusive-OR gate connected in series receives input M and one of the inputs
B.
• When M is at a low logic, we have B⊕ 0 = B. The full-adders receive the value of
B, the input carry is 0, and the circuit performs A plus B.
• When M is at a high logic, we have B⊕ 1 = B' and C0 = 1. The B inputs are
complemented, and a 1 is added through the input carry. The circuit performs the
operation A plus the 2's complement of B.
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12. Binary Incrementer
• The increment micro-operation adds one binary value to the value of binary
variables stored in a register. For instance, a 4-bit register has a binary value 0110,
when incremented by one the value becomes 0111.
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13. Binary Incrementer
• The increment micro-operation is best implemented by a 4-bit combinational
circuit Incrementer. A 4-bit combinational circuit Incrementer can be represented
by the following block diagram.
• A logic-1 is applied to one of the inputs of least significant half-adder, and the
other input is connected to the least significant bit of the number to be
incremented.
• The output carry from one half-adder is connected to one of the inputs of the next-
higher-order half-adder.
• The binary Incrementer circuit receives the four bits from A0 through A3, adds
one to it, and generates the incremented output in S0 through S3.
• The output carry C4 will be 1 only after incrementing binary 1111.
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14. Arithmetic Circuit
• Arithmetic circuits:
• Perform seven different arithmetic operations using a single composite circuit. It
uses a full adder (FA) to perform these operations. A multiplexer (MUX) is used
to provide different inputs to the circuit in order to obtain different arithmetic
operations as outputs.
• 4-bit Arithmetic circuit:
• Consider the following 4-bit Arithmetic circuit with inputs A and B. It can
perform seven different arithmetic operations by varying the inputs of the
multiplexer and the carry (C0).
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16. Topics to be covered in next session 4
• Logic micro operations, Shift micro operations, Arithmetic shift
logic unit
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Thank you!!!