Task 2 Briefing

1. Task 2 Briefing The Design of a Computer Controlled Stop Watch

2. The Technology Used • Based on the Microcontroller card you have built • Controlled by a C program compiled on PC to run on the Microcontroller card. • ASCII characters are used to transfer data between PC and microcontroller • You can use a terminal emulator on the PC, there is no special program for the PC

3. Sample Program • The project worksheet contains a sample program • This is the same program used to test the serial port of your microcontroller card in the lab • Action - every second, the microcontroller sends the time to the PC as a text string over the serial interface . • The time can be displayed on a PC using any terminal program (9600bps, 8 bit, no parity)

4. First Task • You first job is to understand the program and produce documentation for it. • To do this you should: • Compile and run the program • Add comments to the program • Produce Pseudocode for the program • Copies of the commented program and Pseudocode must be submitted to your Supervisor

5. Compiling the Program • The C program on the worksheet is to run on the microcontroller. • This processor uses different machine instructions to the PC • Visual C++ produces machine instructions for the PC - it won’t run on the microcontroller. • CC51 is a C compiler which produces machine instructions which run on the microcontroller

6. The Process of Compiling To compile a program for the microcontroller: • Produce the text C code using any text editor • Use CC51 to compile the program • Make sure there are no errors • Transfer the file produced into the microcontroller (use EPROM programmer) • Compiler produces a HEX format file • Insert the microcontroller in your card and test.

7. Documenting the Program • Before starting to write a new program, you will gain some practice at documenting programs • You should : • Understand what the program does (run it if necessary) • Add comments to the program • Write a Pseudocode description of the program (this should be done before writing a program)

8. Sample Documentation • Consider the program on the microcontroller used with the dice as an example. • Problem : Send a ‘Y’ when the button is pressed and send a ‘N’ when the button is released. At the same time, display any received character on the LEDs. • The following shows 3 ways to describe the problem.

9. action trigger State Diagram

10. Flow Chart

11. Pseudo Code Do forever [while ( true is true )] { while ( key not pressed ) { if (character received) { get character display pattern } } send ‘Y’ while ( key pressed ) {if (character received) { get character display pattern } } send ‘N’ }

12. Comments on Techniques • State Diagram – good graphical technique for describing a process. Doesn’t help much in writing program. Can be used to clarify design before writing pseudocode • Flow Chart – good at describing sequential processes. Doesn’t help much in writing high level programs, but good for machine level coding. • Pseudocode – good at describing complex processes. Helps to write high level code.

13. Creating a Stop Watch Function • You now understand the program ! ! ! • You must modify the program to make it work as a stop watch. • Stop watch control is via the serial interface • Characters entered on the PC keyboard will control the Stop watch <space> hitting the space bar will toggle the Stop watch on and off R resets the display to zero

14. System Diagram 00:01:45 Send ASCII characters of time to display Type <space> to turn on Type <space> to turn off

15. What You Must Do • Firstly, make sure you understand what the Stop watch does – ask if you don’t understand • Modify the Pseudocode for the clock program to make it act as a stop watch • Code this in C • Produce a text file of the program • Compile using CC51 • Load the code into the microcontroller • Test the functionality and debug if necessary

16. Creating a Clock Function • Create a new Pseudocode for a Clock which responds to the following commands : A sets the clock to adjust mode. In adjust mode the clock stops until it receives <CR> Digit in adjust mode, the digits are entered into 1021 the current time <BS> in adjust mode, go back to last entered digit <CR> in adjust mode, returns to clock mode

17. What You Must Do • Again, you must first understand the problem. • In this example, the functionality isn’t so well defined – you have some options, e.g. • What is displayed on the PC in adjust mode • What is displayed on PC when a <BS> is received • When you have decided, write Pseudocode • A State Diagram may help planning • Produce the C program, compile, test and debug

18. Integrating the Functions • When both Stop watch and Clock are working : • Try to combine both Stop watch and Clock into 1 program. • The combined program should respond to the extra commands : C if in Stop watch mode, switch to Clock mode S if in Clock mode, switch to Stop watch mode

19. The Combined Clock • The Clock must keep the right time, even if it is in Stop watch mode. • Hence, clock must keep running in both modes • The program will need a separate variables for the Clock and Stop watch. • The Stop Watch can keep running in Clock mode • The Clock will stop in adjust mode – you can decide what the Stop watch does.

20. Working with the Push Button • So far, all control has been using the PC keyboard sending ASCII characters to the microcontroller. • Here, go back to the Stop watch to make it controlled by the button on the card • Control is : Push button toggles the stop watch on and off Hold button if pushed >1sec, time resets to zero

21. What you must submit • For all 4 programs, you must submit a short report on your program containing: • The Pseudocode • The C program (including comments) • A description of the operation of the program • Submit report when all 4 programs are done. • Your supervisor will check to see your program working before moving to the next stage.

22. For the Brighter Students • It is possible that some groups will finish the three programs within 4 weeks. • We do not expect all groups to finish that quickly. However, you must finish all three programs. • The faster groups can then move on the next project task – implementing a network. • This task has scope for groups to make their own design.