Revision as of 13:35, 21 March 2016

Basics

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 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. When $a \ne 0$, there are two solutions to \(ax^2 + bx + c = 0\) and they are $$x = {-b \pm \sqrt{b^2-4ac} \over 2a}.$$

Timer 0 Registers

TCNT0: Timer/Counter Register 0

TCCR0: Timer/Counter Control Register

TIFR: Timer/Counter Interrupt Flag Register

Timer 1

Timer 2