ATtiny2313 Timers/Counters

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ATtiny2313Timers/Counters

• CS-423
• Dick Steflik

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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)?

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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

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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

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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

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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

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2 Timer/Counter Units

• 8-bit Timer/Counter0 w/PWM
• 16-bit Timer/Counter1
• Timer/Counter1 and Timer/Counter0 prescalers

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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

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8-bit Timer/Counter0
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8-bit Timer/Counter0

• Sample code can be found at
• http//winavr.scienceprog.com/avr-gcc-tutorial/con
  trol-avr-8-bit-timer-counter0-using-avr-gcc.html

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16-bit Timer/Counter1
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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

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16-bit Timer/Counter1

• Sample code can be found at
• http//winavr.scienceprog.com/avr-gcc-tutorial/pro
  gram-16-bit-avr-timer-with-winavr.html

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Prescaler