1. Large Digital Systems

2. Outline  Large Digital Systems  Top-Down Approach  Controller and Data Processor  Flowcharts

3. Outline  Large Digital Systems  Top-Down Approach  Controller and Data Processor  Flowcharts

4. 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.

5. Outline  Large Digital Systems  Top-Down Approach  Controller and Data Processor  Flowcharts

6. 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).

7. 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 TutorialsPass TestsPass Exam Ask questionsPracticeReviseSleep well

8. Outline  Large Digital Systems  Top-Down Approach  Controller and Data Processor  Flowcharts

9. 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.

10. 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

11. 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.

12. Outline  Large Digital Systems  Top-Down Approach  Controller and Data Processor  Flowcharts

13. 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.

14. 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

15. Flowcharts  A decision box is diamond-shaped. It has one entry point and multiple (but mutually exclusive) exit points. choice option Aoption Boption C

16. 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.

17. 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.

18. Flowcharts  An example: Eating a Western meal in oriental style. Drink soup Main course Eat dessert enough? yes no

19. 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 no fitting? BF’s opinion? acceptable poor encouraging insulting no