Register Transfer Flipbook PDF

Register Transfer Logic

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Register Transfer and Micro Operations

contents • Register Transfer Language • Register Transfer • Bus and Memory Transfers • Arithmetic Microoperations

• Logic Microoperations • Shift Microoperations • Arithmetic Logic Shift Unit

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4-1 Register Transfer Language (RTL) • Digital System: An interconnection of hardware modules that do a certain task on the information. • Registers + Operations performed on the data stored in them = Digital Module • Modules are interconnected with common data and control paths to form a digital computer system

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4-1 Register Transfer Language cont. • Microoperations: operations executed on data stored in one or more registers. • For any function of the computer, a sequence of microoperations is used to describe it • The result of the operation may be: – replace the previous binary information of a register or – transferred to another register Shift Right Operation

101101110011

010110111001

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4-1 Register Transfer Language cont. • The internal hardware organization of a digital computer is defined by specifying: • The set of registers it contains and their function • The sequence of microoperations performed on the binary information stored in the registers • The control that initiates the sequence of microoperations

• Registers + Microoperations Hardware + Control Functions = Digital Computer

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4-1 Register Transfer Language cont. • Register Transfer Language (RTL) : a symbolic notation to describe the microoperation transfers among registers Next steps: – Define symbols for various types of microoperations, – Describe the hardware that implements these microoperations

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4-2 Register Transfer (our first microoperation) • Computer registers are designated by capital letters (sometimes followed by numerals) to denote the function of the register • R1: processor register • MAR: Memory Address Register (holds an address for a memory unit) • PC: Program Counter • IR: Instruction Register • SR: Status Register

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4-2 Register Transfer • The individual flip-flops in an n-bit register are numbered in sequence from 0 to n-1 (from the right position toward the left position)

7 6 5 4 3 2 1 0

R1

Register R1

Showing individual bits

A block diagram of a register

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4-2 Register Transfer Other ways of drawing the block diagram of a register: 15

0

PC Numbering of bits

15

Upper byte

PC(H)

87

0

PC(L)

Lower byte

Partitioned into two parts

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4-2 Register Transfer

• Information transfer from one register to another is described by a replacement operator: R2 ← R1 • This statement denotes a transfer of the content of register R1 into register R2 • The transfer happens in one clock cycle • The content of the R1 (source) does not change • The content of the R2 (destination) will be lost and replaced by the new data transferred from R1 • We are assuming that the circuits are available from the outputs of the source register to the inputs of the destination register, and that the destination register has a parallel load capability

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4-2 Register Transfer • Conditional transfer occurs only under a control condition • Representation of a (conditional) transfer P: R2 ← R1 • A binary condition (P equals to 0 or 1) determines when the transfer occurs • The content of R1 is transferred into R2 only if P is 1

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4-2 Register Transfer Hardware implementation of a controlled transfer: P: R2 ← R1 Control P Circuit

Block diagram:

Load

R2

Clock

n

R1

t Timing diagram

t+1

Clock Load Transfer occurs here

Synchronized with the clock

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4-2 Register Transfer Basic Symbols for Register Transfers Symbol Description Examples Letters & Denotes a register numerals Parenthesis ( ) Denotes a part of a register

MAR, R2

Arrow ←

Denotes transfer of information

R2 ← R1

Comma ,

Separates two microoperations

R2 ← R1, R1 ← R2

R2(0-7), R2(L)

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