Exam zone
ATtiny2313 Timers/Counters
CS-423 Dick Steflik
What Do You Use Timers For?
Timing of events (internal or external)
Scheduling Events
Measuring the width of a pulse
Speed control of motors (PWM)
Generation of complex waveforms
Frequency generation (sounds)
The concept of using a timer/counter
Counters run asynchronously to your code Can be setup to start based on an internal or external event
Can generate interrupts
Can signal to a pin
Example
To time a piece of code:
Initial the counter to 0, have it interrupt on overflow
Interrupt handler should count overflows
Start the counter
Run your code
At end of code read counter and add to number of overflows to get total time
Example
To time an incoming pulse/event:
Setup interrupts on rising and falling edge of pulse and overflow of counter
In handler for rising edge start counter
In handler for overflow, count the overflows
In handler for falling edge read counter and add overflows to get time of pulse/event
Example
Motor control:
Use counter to generate a pulse train to control speed of DC motors
Full speed = full power (infinitely wide pulse Low speed = narrow pulses with wide down time 50% speed = equal up and down times
Can only control very small motoers directly, must use high power transistors to drive bigger motors
This is came idea as intermittent wipers on a car
2 Timer/Counter Units
8-bit Timer/Counter0 w/PWM
16-bit Timer/Counter1
Timer/Counter1 and Timer/Counter0 prescalers
8-bit Timer/Counter0
Single channel counter
Frequency Generator
External Event Counter
10-bit clock prescaler
Only used with internal clock
Scale by: 1, 8, 64, 256, 1024
8-bit Timer/Counter0
8-bit Timer/Counter0 ď Ź ď Ź
Sample code can be found at: http://winavr.scienceprog.com/avr-gcc-tutorial/control-avr-8-bit-timer-counter0-using-avrgcc.html
16-bit Timer/Counter1
Modes of Operation
Normal Mode – always counts up, no clear, counter just overruns
Clear Timer on Compare match (CTC mode)
Fast PWM Mode
Phase Correct PWM mode
Phase and Frequence Correct PWM mode
16-bit Timer/Counter1 ď Ź ď Ź
Sample code can be found at: http://winavr.scienceprog.com/avr-gcc-tutorial/program-16-bit-avr-timer-withwinavr.html
Prescaler