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Computer Organization
Unit - II

Register Transfer Language

1. Register Transfer

Register Transfer describes the operations on the data stored in registers and how data is moved from one register to another. It involves signals that control the movement of data between registers.

  • Example: If R1 contains the value 5, a transfer operation moves this value to R2 based on a control signal.

2. Bus and Memory Transfer

2.1 Bus Transfer

A Bus is a communication system that transfers data between components inside a computer, or between computers. It is usually shared by multiple devices to communicate.

Three-stage Bus Buffers: Buffers control data flow between devices in multiple stages for proper communication.

2.2 Memory Transfer

Memory transfer refers to moving data between memory and registers or between different memory locations. It often uses buses to carry the data.

  • Example: Transferring the contents of memory location A to memory location B via the data bus.

3. Arithmetic Micro-Operations

Arithmetic micro-operations perform simple arithmetic operations on numeric data stored in registers.

3.1 Binary Adder

A Binary Adder adds two binary numbers and produces a sum and a carry bit.

  • Example: Adding binary 1101 and 1011:
  1101
+ 1011
------
  11000 (Sum = 1000, Carry = 1)

3.2 Binary Adder-Subtractor

This circuit can perform both addition and subtraction using a control signal. Subtraction is achieved by adding the 2's complement of the number.

  • Example: To subtract 5 from 7, we add the 2’s complement of 5 to 7.

3.3 Binary Incrementer

A Binary Incrementer adds 1 to a binary number.

  • Example: Incrementing 0111:
0111 + 1 = 1000

3.4 Arithmetic Circuit

An Arithmetic Circuit performs a variety of arithmetic operations like addition, subtraction, increment, and decrement.

4. Logic Micro-Operations

Logic micro-operations perform bitwise logical operations (AND, OR, NOT, etc.) on registers.

4.1 List of Logic Micro-Operations

  • AND: Performs logical AND between two registers.
  • OR: Performs logical OR between two registers.
  • NOT: Complements the bits in a register.
  • XOR: Performs logical XOR between two registers.

4.2 Hardware Implementation

Logic micro-operations can be implemented using logic gates. Each operation is performed by corresponding hardware logic.

5. Shift Micro-Operations

Shift micro-operations move bits in a register to the left or right. Shifts can be:

  • Logical Shift: Shifts bits left or right, and fills the empty positions with zeros.
  • Arithmetic Shift: Shifts bits while preserving the sign bit.
  • Circular Shift: Rotates the bits so that shifted-out bits are reinserted into the opposite end.

5.1 Hardware Implementation

Hardware implementation of shift operations uses shift registers.

  • Example of Left Shift:
1010 (binary) << 1 = 0100

6. Arithmetic Logic Shift Unit

An Arithmetic Logic Shift Unit combines arithmetic operations, logic operations, and shift operations into a single unit. This unit can perform all these operations based on control signals.

The Arithmetic Logic Shift Unit can be controlled to perform:

  • Addition
  • Subtraction
  • Logical operations (AND, OR, NOT)
  • Shifts (left, right, circular)
Unit - IUnit - III