Large Digital Systems

Large Digital Systems

Outline

Large Digital Systems Top-Down Approach Controller and Data Processor

Flowcharts

Outline

Large Digital Systems Top-Down Approach Controller and Data Processor

Flowcharts

Large Digital Systems

In both combinational and sequential circuit design: small circuits via gate-level design (truth tables, K maps, etc) large circuits via block-level design (MSI components, etc.)

However, larger digital systems need more abstract and systematic design techniques.

One such systematic design method has the following characteristics: top-down approach separation of controller from controlled hardware develop an overall architecture (at block levels) before

proceeding into the details of hardware.

Outline

Large Digital Systems Top-Down Approach Controller and Data Processor

Flowcharts

Top-Down Approach

Top-down approach is immensely important for large complex system (whether hardware, software, or manual systems).

Emphasis on macroscopic view, starting from original problem and gradually refine it towards solution.

Steps for a top-down design procedure: Specify the problem clearly (at global/top level without

unnecessary details). Break the problem into smaller sub-problems. Repeat the process until sub-problems are small enough to

be solved directly (implementable).

Top-Down Approach

Corresponds to goal-directed approach. State goal, then find sub-goals to solve main goal. Repeat until sub-goals are directly solvable.

Pass DLD

Do Tutorials Pass Tests Pass Exam

Ask questions Practice Revise Sleep well

Outline

Large Digital Systems Top-Down Approach Controller and Data Processor

Flowcharts

Controller & Data Processor

Digital systems are typically processors of information.

They store data through flip-flops, registers and memory, and process them using combinational circuits like adders, multipliers, etc.

These processing may pass through complicated sequences.

Controller & Data Processor

A digital system consists of two components A control algorithm (controller) and An architecture (data processor)

Control unit (Controller)

Data Processor

(Architecture)

Commands

Input data

External command

Status condition

Output data

Controller & Data Processor

Separation of the controller operations from the data processing operations Control operations give commands that direct the data

processing operations to accomplish the desired tasks. Data processing operations manipulates the data

according to requirements.

A mechanical analogy: Automobile. Car (data processor): transports people from one location

to another. Driver (controller): gives instructions to car to achieve

objective.

Outline

Large Digital Systems Top-Down Approach Controller and Data Processor

Flowcharts

Flowcharts

Flowcharts: a tool for precise description of algorithms/procedures.

Specify tasks to perform and their sequencing.

Main symbols: Operation box: contains tasks/operations to perform. Decision box: alternative actions based on decisions to be

taken. Arrows: indicate appropriate sequencing.

Flowcharts

An operation box is rectangular in shape, and is used to specify one or more subtasks to be performed. It has at most one entry point and one exit point.

Sub-task or operation to perform

Flowcharts

A decision box is diamond-shaped. It has one entry point and multiple (but mutually exclusive) exit points.

choice

option A option B option C

Flowcharts

Sequential flow: simplest type of sequencing; tasks are done in sequential order.

An example: Eating a 3-course Western meal.

Drink soup

Main course

Eat dessert

Boxes are connected by lines with arrows. Lines without arrows are sometimes used. In the absence of arrows, the default flow direction is top-to-bottom and left-to-right.

Flowcharts

Iteration: some tasks/operations may be repeatedly/iteratively done.

This is achieved through the loop-back in the flowchart.

Decision box is used to determine when to terminate the loop.

Flowcharts

An example: Eating a Western meal in oriental style.

Drink soup

Main course

Eat dessert

enough?

yes

no

Flowcharts

Flowcharts can be used to implement complex decisions.

get BF to buy

nice color & style?

yes

no

reject

test out

affordable?

made in Europe?

yes

yesno

fitting?

BF’s opinion?

acceptable

poor

encouraging

insulting

no