Compare Mode w/ Atmel Studio 7 & UNO (Episode#07)

If we look at the CCP Module we have Capture (as Input) allows us to measure the time between two events; Compare (as Output) allows the generation of a signal on the CCPx pin at predefined time intervals: it is useful if we want to generate a programmable width pulse on the pin (example control a drone) and lastly PWM (output) generation of a pulsed square wave signal with ON and OFF cycle width control (10-bit resolution). Well in the previous episodes we saw the common mode via Timer1 interrupt; now we will enter the CCP module for good! In this post we’ll cover COMPARE! welcome!

Step#01→ As usual in this serie Copy/Paste the previous code to a new project on Atmel Studio 7. Good!

In order to change the nomal mode to compare mode look at data sheet page 132 upward; Table 16–4. Waveform Generation Mode Bit Description.

All we need to set is the bit WGM12 that is on TCCR1B byte:

TCCR1B |=   (1 << CS12) | (1 << WGM12);

Step#02→ If you look again the main caracteristics of Atmega ATmega/328/P you’ll understand there are two channel on Compare outputs on OCxA and OCxB. [more detail see my post about ATtiny85].

We should also change the kind of interruption we need. We had the Overflow Timer1 Interrupt and we will switch to Output Compare on Channel 1. Now here’s a new technique in Atmel Studio 7; Follow this tip with me! Place the cursor over the TOIE1 in:

TIMSK1 |= (1 << TOIE1);

Alt + G and you’ll be redirected for iom328p.h. Right below copy OCIE1A and past in the code above n’you’ll get:

TIMSK1 |= (1 << OCIE1A);

Step#03 → Use the same technique to find the Compare vector A; Place the cursor inside TIMER1_OVF_vect:

ISR(TIMER1_COMPA_vect) 
{
  LedToggle;
}

Step#04 → Now the function representing the frequency we wanted to overflow at:

void Timer_Frequency(uint8_t freq)
{}

Step#05 → Transfer this part from Main inside this brand new function:

void Timer_Frequency(uint8_t freq)
{
TCCR1B |=   (1 << CS12) | (1 << WGM12);
TIMSK1 |= (1 << OCIE1A);
}

You can clear the code up! Good!

Step#06→ Rearrage the formula found on page 123 and you’ll get:

OCRnA = (F_CPU/(Frequency * 2 * N) - 1)

OCRnA — Output Compare pin we want to set it’s frequency;

F_CPU — our Arduino 16MHz cycle;

N — Prescale used (246)

And put this right in our code make we remember what we’ll need to do ;-)

Step#07 → substitute the real values in the formula and…

OCR1A = (F_CPU/(freq * 2 * 256) - 1);

Step#08 → And finally make a call to this methods in main:

int main(void)
{
  Timer_Frequency(10);
...
}

Step#09 → There you have it!

Just F7, and Sendo To Arduino UNO.

Code?

https://github.com/giljr/avr/tree/master/atmel

There you have it!

Look for Episode #7:-)

In the next post we will use AVRs timers to generate some PWM!

Take care!See you soon!

References & Credits

Atmel Code base Github

Follow along with the entire ‘Getting Started with AVR’ series: http://bit.ly/GettingStartedwithAVR

→Goto Episode#08

Complete Serie:

#00 HowTo-Load-Into-Arduino-AS7

#01_Hello-World

#02_Presents-AVR-Freaks

#03_Pressing-Button

#04_Pin-Change-Interrup

#05_Battery-Driven-App

#06_Timer Counter

#07_Compare Mode

#08

#09

#10