Chapter 7 – Registers and Register Transfers

Part 1 – Registers, Microoperations and Implementations

Logic and Computer Design Fundamentals

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Overview

Part 1 - Registers, Microoperations and Implementations• Registers and load enable• Register transfer operations• Microoperations - arithmetic, logic, and shift• Microoperations on a single register

Multiplexer-based transfers Shift registers

Part 2 - Counters, Register Cells, Buses, & Serial Operations

Part 3 – Control of Register Transfers

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Registers

Register • a collection of binary storage elements • included a set of flip-flop• n-bit register store n-bit binary information

Frequently used to perform simple data storage and data movement and processing operations

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7-1 Register and Load Enable

Register with load enable

by clock gating

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7-1 Register and Load Enable

Register with load enable

directly through input

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7-2 Register transfer

Large digital systems are hard to be designed by using state table in Chap. 5

Large digital systems are often designed by modular, hierarchical approach

Large digital systems are partitioned into two types of modules

• Datapath: performs data-processing operations

• Control unit: determine the sequence of those operations

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7-2 Register transfer

The registers are assumed to be basic components of the digital system

Register transfer operation: movement on the data stored in register and the processing performed on the data

Three basic components• The set of registers in digital systems• The operations performed on the data• Control on the sequence of operations

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7-3 Register Transfer Operations

Notation for register: uppercase letters (sometime followed by numbers)• AR: address register• PC: program counter• IP: instruction register• R2: the register 2

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7-3 Register Transfer Operations

Data transfer from a register to another one • R2 ←R1

Data transfer with conditions• If (K1=1) then (R2 ←R1)• K1: R2 ←R1

Hardware implementation

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7-3 Register Transfer Operations

More register transfer operation executed at the same time:

K3: R2 ←R1, R1 ←R2

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7-4 A note for VHDL and Verilog

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7-5 Microoperation

An elementary operations performed on data stored in registers or in memory.• Transfer • Arithmetic• Logic: perform bit manipulation on data in

register Bitwise AND, Bitwise OR ….

• Shift

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Arithmetic Microoperations

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Arithmetic Microoperations

The control variable X selects the operation, and the control variable K1 loads the result in to R1.

211:1 RRRKX

1211:1 RRRKX

Fig. 7.6 Implementation