Microprogrammed Control in Digital Systems

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Questions and Answers

What distinguishes microprogrammed control from hardwired control?

It uses fixed logic circuits

It involves changing wiring among components for modifications

It stores control information in a special memory (correct)

It operates at a fast speed

Which type of control is more flexible in terms of making changes or modifications?

Control with fixed logic circuits

Hardwired control

Control requiring changes in wiring

Microprogrammed control (correct)

What is a drawback of microprogrammed control in terms of operational speed?

Slower mode of operation (correct)

Requires changing wiring

Fast mode of operation

Operates at the speed of light

Which aspect makes microprogrammed control advantageous for making modifications?

Changing memory contents Signup and view all the answers

What is a key characteristic of hardwired control in its implementation?

Implements control logic with gates and flip-flops Signup and view all the answers

Why does microprogrammed control offer more flexibility compared to hardwired control?

Changes are made by altering memory contents Signup and view all the answers

What is the purpose of the control unit in a digital system?

Initiate a series of sequential steps of operations Signup and view all the answers

How are the control variables represented at any given time in a digital system?

As a long string of binary codes Signup and view all the answers

What is a microprogrammed control unit?

A control unit whose binary control variables are stored in memory Signup and view all the answers

What is each word in the control memory called in microprogrammed control?

Microinstruction Signup and view all the answers

What does the Control Address Register (CAR) specify in a microprogrammed control system?

The address of the microinstruction Signup and view all the answers

How is the location of the next microinstruction generated in microprogrammed control?

By the sequencer Signup and view all the answers

What is one of the typical functions of a microprogrammed sequencer?

Setting the external address as the new control address register (CAR) Signup and view all the answers

What does the microinstruction do to initiate control operations?

Loads an initial address into the control address register (CAR) Signup and view all the answers

In microprogrammed control, what does the microprogram counter (µPC) typically do?

Receive a new address at every clock pulse transition Signup and view all the answers

What controls the sequence and branching in a microprogrammed control unit?

Address Control Memory (CM) Signup and view all the answers

What is the purpose of the microinstruction register (µIR) in microprogramming?

To hold the microinstruction during execution Signup and view all the answers

Which component receives a new address at any given clock pulse transition in microprogrammed control?

Microprogram Counter (µPC) Signup and view all the answers

Study Notes

Control Unit Design

The logic design of a digital system can be divided into two parts: Data path design (Data Processor) and Control Unit design.

Data Path Design

Deals with the design of digital circuits that perform data processing operations (Arithmetic, logic, shift operations)

Control Unit Design

Deals with the design of the control circuit that supervises the operations and determines the sequence in which they are executed.

Hardwired Control

Uses fixed logic circuits to generate control signals
Advantage: Fast mode of operation
Disadvantage: Requires changes in wiring among various components if the design has to be modified

Microprogrammed Control

The control information is stored as 1's and 0's in a special memory
Advantage: More flexible, changes can be made by changing the contents of the memory
Disadvantage: Slow mode of operation, extra hardware cost

Microprogrammed Control Unit

A control unit whose binary control variables are stored in a memory
Each word in control memory is called a microinstruction
A sequence of microinstructions constitutes the microprogram
The control memory can be either a ROM or RAM

Generation of Microprogrammed Control

Control address register (CAR) or Microprogram Counter (µPC): specifies the address of the microinstruction
Control data register (CDR) or Microinstruction Register (µIR): holds the microinstruction read from memory
The location of the next microinstruction is generated by the sequencer

Microprogrammed Sequencer

Typical functions: increment the control address register (CAR) by one, transfer an external address into CAR, load an initial address into CAR to start the control operations

Microprogrammed Control Unit Components

Microprogram Counter (µPC)
Control Memory (CM)
Microinstruction Register (µIR)
Decoder
Data processing unit
External Conditions
External Address
MUX

Microprogram Example

Example of a microprogrammed control unit with external conditions and addresses
Microprogram consists of microinstructions with control signals to the decoder and data processing unit

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Description

This quiz covers the concept of microprogrammed control in digital systems, focusing on the purpose of the control unit, generating control words, and programming control words to initiate various components in a data processor.