1. Interrupts Microprocessor and Interfacing261214

2. Example: Writing a Game Need to Check Keyboard Input

3. Method 1: Using a LoopProgram keeps checking for keyboard input While (1) [ If Key = Right Then moveRight ElseIf Key = Left Then moveLeft End If ]

4. Mothod II: Use KeyPress EventRuns only when there is a keyboard interrupt KeyPressEvent(Key) If Key = Left Then MoveLeft ElseIf Key = Right Then MoveRight End If End Subroutine

5. What’s the Difference BetweenMethod I - Method II ?

6. Method I : Software Polling Method II : Event or Interrupt Driven

7. I/O Handling Techniques • Software Polling • Interrupts • Direct Memory Access (DMA)

8. Benefits of Using Interrupts • Consumes much less CPU • Especially when interrupt generated by hardware • Cleaner & Simpler Code • Allows Basic Parallel Processing

9. Exercise: Program a PIC Microcontroller • Blink an LED every 0.5 sec • Also receives serial data from the computer What’s wrong with this program? While (1) { output_toggle(LED); delay_ms(500); data = getchar(); }

10. A better program, but not best While (1) { output_toggle(LED); delay_ms(500); if (kbhit()) { data = getchar(); } }

11. How do we fix the problem? Available Commands • Getchar() – wait and return serial data • Output_toggle(LED) • Time() – returns current time (in ms) • Kbhit() – returns true if serial data is available

12. Solution Software Polling IntcurrentTime; Char data; startTime = time(); While (1) { if (time() – startTime > 500) { output_toggle(LED); startTime = time(); } if (kbhit()) { data = getchar(); } }

13. Same Program with Timer Interrupt timerISR() { output_toggle(LED); } Main() { setupTimer(); while (1) { data = getchar(); } }

14. Interrupt Handling

15. Multi-Interrupt Handling