ECE 447: Lecture 8

1. ECE 447: Lecture 8 Timer System

2. ECE447: Timer I/O Pins PA0 - Input Capture 3 (IC3) PA1 - Input Capture 2 (IC2) PA2 - Input Capture 1 (IC1) PA3 - Input Capture 4/ Output compare 5 (IC4/OC5) PA4 - Output Compare 4 (OC4) PA5 - Output Compare 3 (OC3) PA6 - Output Compare 2 (OC2) PA7 - Pulse Accumulator Input (PAI)

3. Example for Input Capture 1 Unusual procedure!!! Set a flag Clear a flag #define IC1F 0x04 Cannot be done in software!!! TFLG1 = IC1F; Set by a preselected edge at the PA2 input Cleared by writing 1 to the corresponding bit location!!! ECE 447: Setting and Clearing Event Flags

4. ECE447: Measuring Pulse Widths 100 s < width < 32.768 ms stop start width  100 s stop start width  32.768 ms stop start Timer overflows

5. ECE 447: Measuring intervals <216 clock cycles FFFF stop start 0

6. ECE 447: Measuring intervals <216 clock cycles (overflow) 1 2 FFFF start stop 0

7. ECE 447: Measuring intervals >216 clock cycles 1 2 N=3 FFFF stop R start 0

8. ECE 447: Measuring intervals >216 clock cycles 3 N=4 1 2 FFFF R1 start R1+R2=R stop 0 R2

9. ECE447: Class Exercise Output Compare Write a program that generates a square wave with the frequency of 50 Hz and the duty cycle 25% at pin PA6 of MC68HC11. (use polling) Write the same function using interrupts.

10. ECE447: Class Exercise Delay Function Write a function in C that generates a delay specified as an argument to this function. Assume that the delay is given in the number of clock cycles. (use polling) Write the same function using interrupts.

11. ECE447: Class Exercise Pulse Accumulator Write a function in C that counts the number of pulses at the input PAI during the period of 30 ms. Write the same function using interrupts.