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Outline Large Digital Systems Top-Down Approach Controller and Data Processor FlowchartsTRANSCRIPT
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.
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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