Transcript cs.binghamton.edu

ATtiny2313
Timers/Counters
CS-423
Dick Steflik
What Do You Use Timers For?
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Timing of events (internal or external)
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Scheduling Events
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Measuring the width of a pulse
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Speed control of motors (PWM)
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Generation of complex waveforms
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Frequency generation (sounds)
The concept of using a
timer/counter
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Counters run asynchronously to your code
Can be setup to start based on an internal or
external event
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Can generate interrupts
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Can signal to a pin
Example
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To time a piece of code:
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Initial the counter to 0, have it interrupt on overflow
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Interrupt handler should count overflows
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Start the counter
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Run your code
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At end of code read counter and add to number of
overflows to get total time
Example
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To time an incoming pulse/event:
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Setup interrupts on rising and falling edge of pulse
and overflow of counter
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In handler for rising edge start counter
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In handler for overflow, count the overflows
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In handler for falling edge read counter and add
overflows to get time of pulse/event
Example
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Motor control:
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Use counter to generate a pulse train to control
speed of DC motors
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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
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8-bit Timer/Counter0 w/PWM
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16-bit Timer/Counter1
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Timer/Counter1 and Timer/Counter0 prescalers
8-bit Timer/Counter0
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Single channel counter
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Frequency Generator
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External Event Counter
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10-bit clock prescaler
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Only used with internal clock
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Scale by: 1, 8, 64, 256, 1024
8-bit Timer/Counter0
8-bit Timer/Counter0
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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
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Normal Mode – always counts up, no clear, counter just overruns
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Clear Timer on Compare match (CTC mode)
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Fast PWM Mode
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Phase Correct PWM mode
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Phase and Frequence Correct PWM mode
16-bit Timer/Counter1
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Sample code can be found at:
http://winavr.scienceprog.com/avr-gcc-tutorial/program-16-bit-avr-timer-withwinavr.html
Prescaler