How To Load The Period Register For Timer Counter Atmel Atxmega128a1u

1 Nuts
2 Timer 0 Basics
3 Timer 0 Example
- 3.ane Code
4 Timer 1 Nuts
five Timer 1 Example
- 5.1 Code
6 Timer 2
7 Downloads

Basics

Timers come in handy when you want to set some time interval like your warning. This tin exist very precise to a few microseconds.

Timer/Counter Unit

Timers/Counters are essential part of any mod MCU. Recollect it is the same hardware unit inside the MCU that is used either as Timers or Counter. Timers/counters are an independent unit within a micro-controller. They basically run independently of what job CPU is performing. Hence they come in very handy, and are primarily used for the following:

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

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

Timer 0 Basics

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

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

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

The configuration of the Timer can be set using the TCCR0 register shown below. With this you tin can basically select 2 things:

The Frequency of the Clock Source with CS02, CS01, CS00 bits.
The mode of the timer. For the first example we will use information technology in normal mode where it ticks from zero to the highest value(255)

Timer Counter Control Register 0
TCCR0
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	i	Clk/64
1	0	0	Clk/256
ane	0	one	Clk/1024
i	i	0	Clk/T0-Falling edge
ane	1	1	Clk/T0-Rising Edge

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

The Timer/counter Interrupt Flag Register(TIFR) holds the two basic flags we demand the TOV and OVF. Other $.25 correspond to the timer interrupts, which we will expect at in some other tutorial.

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

Timer 0 Instance

Toggle LED connected to PD4 every 100msec using Timer Cipher with 1024 pre-scalar in normal mode.

What is the Max delay Timer 0 overflow generates? Okay, lets calculate. The Explore Ultra AVR dev lath comes with a 16MHz on board crystal and the fuse bits are ready appropriately. If we use the highest pre-scalar of 1024, calculation shows it can generate a delay of 16milli seconds every time timer zero overflows.

$$Ftimer = CPU Frequency/Prescalar $$ $$Ftimer = 16MHz/1024 = 15.625KHz $$ $$Ttick = 1/ fifteen.625K = 64 \mu seconds$$ $$Ttotal = 64\mu due south X 255 = 16ms$$

Of-course 16ms is non enough, so the side by side obvious question is:
How many times should the timer overflow to generate a delay of approximately 100msec?

$$ OverFlowCount = 100ms/16ms = half dozen.25 ≈ six $$

Now let's write a elementary program which will toggle a port pin (PD4) after the timer 0 overflows 6 times.

Load TCNT0 with 0x00
Set CS00 and CS02 bits in TCCR0 register. This will starting time the timeWe will calculate the tick time in merely a moment.r at Clk/1024 speed.
Monitor the TOV0 flag in the TIFR0 register to check if the timer has over-flowed, keep a timerOverFlowCount.
If timerOverFlowCount >= 6, toggle the led on PD4 and reset the count

Code

Timer 1 Basics

The Timer 1 is 16 chip, that means it can count from 0 to $$2^{16} = 65536$$. Hence the Timer/Counter 1 is a 16 fleck registered formed out of TCNT1H and TCNT1L equally shown below.

Timer/Counter ane
TCNT1H								TCNT1L
D15	D14	D13	D12	D11	D10	D9	D8	D7	D6	D5	D4	D3	D2	D1	D0

Timer three also has ii control registers which allow united states of america to configure it and utilize information technology in whatsoever mode you wish.

Timer Counter Control Register 1A
TCCR1A
D7	D6	D5	D4	D3	D2	D1	D0
COM1A1	COM1A0	COM1B1	COM1B0	FOC1A	FOC1B	WGM11	WGM10

Timer Counter Control Register 1B
TCCR1B
D7	D6	D5	D4	D3	D2	D1	D0
ICNC1	ICES1	-	WGM13	WGM12	CS12	CS11	CS10

D2	D1	D0	Clock Source
CS12	CS11	CS10	Freq
0	0	0	No Clock (Stopped)
0	0	1	Clk
0	1	0	Clk/eight
0	1	i	Clk/64
1	0	0	Clk/256
1	0	i	Clk/1024
1	1	0	Clk/T1-Falling edge
one	1	ane	Clk/T1-Rising Edge

Yes, and indeed nosotros take a Flag register which will tell us the status of Timer 1 equally shown beneath.

Timer/Counter 1 Flag Annals
TIFR
D7	D6	D5	D4	D3	D2	D1	D0
OCF2	TOV2	ICF1	OCF1A	OCF1B	TOV1	OCF0	TOV0

Timer i Instance

Let us repeat the case of Timer 0 of toggling PD4 every 100ms. This time since it is a 16 bit timer, let's see what is the max delay information technology generates with a pre-scalar of 1024.

$$Ftimer = CPU Frequency/Prescalar $$ $$Ftimer = 16MHz/1024 = xv.625KHz $$ $$Ttick = 1/ fifteen.625K = 64 \mu seconds$$ $$Ttotal = 64\mu due south X 65536 = 4 seconds$$

So that is 4 secs! We just need 100 msec so, $$100ms/64\mu s = 1562 = 0x061A$$

This time, instead of using the overflow flag, it's use Output Compare Register (OCR) and the related flag.

So the with the following steps we should be able to generate the required delay.

Load OCR1H with 0x3d and OCR1L with 0x09
Run the timer with pre-scalar of 1024 by setting CS12 and CS10 $.25.
Monitor OCF flag and if it is set, toggle the led
Reset the TCNT1L and TCNT1H values to goose egg and repeat steps i to 3.

Code

Timer two

Well, timer 2 is pretty similar to the timers covered above. Give it a shot, should you've any questions do comment below.

Timers are independent units from the CPU. Hence if we employ timers with Interrupts it can brand the CPU free from polling the flags every-time. This is the way they are used normally. Check AVR Timer Interrupts tutorial where we volition comprehend all of that.