Difference between revisions of "AVR Timer programming"

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Atmega32 has 3 timer units, timer 0, timer 1 and timer 2 respectively. Let us start our exploration with timer 0.  
 
Atmega32 has 3 timer units, timer 0, timer 1 and timer 2 respectively. Let us start our exploration with timer 0.  
 
=Timer 0 =
 
=Timer 0 =
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[[File:Timer 0.png|center]]
 
Timer 0 is a 8 bit timer. It basically means it can count from 0 to 2^8 255. The operation of timer 0 is straight forward. The TCNT0 register hold the timer Count and it is incremented on every timer '''"tick"'''. If the timer is turned on it ticks from 0 to 255 and overflows.  If it does so, a Timer OverFlow Flag(TOV) is set.  
 
Timer 0 is a 8 bit timer. It basically means it can count from 0 to 2^8 255. The operation of timer 0 is straight forward. The TCNT0 register hold the timer Count and it is incremented on every timer '''"tick"'''. If the timer is turned on it ticks from 0 to 255 and overflows.  If it does so, a Timer OverFlow Flag(TOV) is set.  
  
 
You can as well load a count value in TCNT0 and start the timer from a specific count. Another interesting feature is that a value can be set in the Output Compare Register (OCR0), and whenever TCNT0 reaches that value, the Output Compare Flag (OCF0) flag is Set.
 
You can as well load a count value in TCNT0 and start the timer from a specific count. Another interesting feature is that a value can be set in the Output Compare Register (OCR0), and whenever TCNT0 reaches that value, the Output Compare Flag (OCF0) flag is Set.
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When $a \ne 0$, there are two solutions to \(ax^2 + bx + c = 0\) and they are
 
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$$x = {-b \pm \sqrt{b^2-4ac} \over 2a}.$$
 
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[[File:Timer 0.png|center]]
 
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===Timer 0 Registers===
 
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====TCNT0: Timer/Counter Register 0====
 
 
{| style="text-align:center;" class="table table-responsive table-bordered"  
 
{| style="text-align:center;" class="table table-responsive table-bordered"  
 
!colspan = '8'|TCNT0
 
!colspan = '8'|TCNT0
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|}
 
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====TCCR0: Timer/Counter Control Register====
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{| class="table table-responsive table-bordered" style="float:center;"
 
{| class="table table-responsive table-bordered" style="float:center;"
 
!colspan = '8'|TCCR0
 
!colspan = '8'|TCCR0
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|+ Timer Counter Control Register 0
 
|D7||D6||D5||D4||D3||D2||D1||D0
 
|D7||D6||D5||D4||D3||D2||D1||D0
 
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====TIFR: Timer/Counter Interrupt Flag Register====
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{| class="wikitable floatright" style="float:right; background-color:#3DA8BB;"
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{| class="table table-responsive table-bordered" style="float:right;"
 
!colspan = '8'|TIFR
 
!colspan = '8'|TIFR
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|+Timer/Counter 0
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|+Timer/Counter 0 Flag Register
 
|D7||D6||D5||D4||D3||D2||D1||D0
 
|D7||D6||D5||D4||D3||D2||D1||D0
 
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Revision as of 13:40, 21 March 2016

Basics

Timer/Counter Unit

Timers come in handy when you want to set some time interval like your alarm. This can be very precise to a few microseconds. Timers/Counters are essential part of any modern MCU. Remember it is the same hardware unit inside the MCU that is used either as Timers or Counter. Timers/counters are an independent unit inside a micro-controller. They basically run independently of what task CPU is performing. Hence they come in very handy, and are primarily used for the following:

  • Internal Timer: As an internal timer the unit, ticks on the oscillator frequency. The oscillator frequency can be directly feed to the timer or it can be pre-scaled. In this mode it used generate precise delays. Or as precise time counting machine.
  • External Counter: In this mode the unit is used to count events on a specific external pin on a MCU.
  • Pulse width Modulation(PWM) Generator: PWM is used in speed control of motors and various other applications.

Atmega32 has 3 timer units, timer 0, timer 1 and timer 2 respectively. Let us start our exploration with timer 0.

Timer 0

Timer 0.png

Timer 0 is a 8 bit timer. It basically means it can count from 0 to 2^8 255. The operation of timer 0 is straight forward. The TCNT0 register hold the timer Count and it is incremented on every timer "tick". If the timer is turned on it ticks from 0 to 255 and overflows. If it does so, a Timer OverFlow Flag(TOV) is set.

You can as well load a count value in TCNT0 and start the timer from a specific count. Another interesting feature is that a value can be set in the Output Compare Register (OCR0), and whenever TCNT0 reaches that value, the Output Compare Flag (OCF0) flag is Set.


TCNT0
Timer/Counter 0
D7 D6 D5 D4 D3 D2 D1 D0


TCCR0
Timer Counter Control Register 0
D7 D6 D5 D4 D3 D2 D1 D0
FOC0 WGM00 COM01 COM00 WGM01 CS02 CS01 CS00
D2 D1 D0 Clock Source
CS02 CS01 CS00 Freq
0 0 0 No Clock (Stopped)
0 0 1 Clk
0 1 0 Clk/8
0 1 1 Clk/64
1 0 0 Clk/256
1 0 1 Clk/1024
1 1 0 Clk/T0-Falling edge
1 1 1 Clk/T0-Rising Edge


D6 D3 PWM
WGM00 WGM01 Mode
0 0 Normal
0 1 CTC (Clear timer on compare match)
1 0 PWM (Phase correct)
1 1 Fast PWM


TIFR
Timer/Counter 0 Flag Register
D7 D6 D5 D4 D3 D2 D1 D0
OCF2 TOV2 ICF1 OCF1A OCF1B TOV1 OCF0 TOV0

Timer 1

Timer 2

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