没有引脚控制的Arduino定时器中断

Question

Help me please with Arduino Timer Interrupts.

How to start timer OCR0A or OCR2A without pin-controlling to start my custom function output1Display() ? Interval of 1 ms.

ATmega328P, 8MHz quartz.

Answer 1

First of all, you should search for and download the 328P datasheet, which covers the details of timer setup. I suggest you use Timer2 only, since Timer0 is used for other things you probably don't want to mess up.

Since the datasheet can be confusing when you are starting out, here's what you need: First, you need to select a clock scaler. Timer2 can count the main clock directly, or divided by 8, 32, 64, 128, 256, or 1024 for slower rates. Note that Timer2 uses an 8-bit counter, so the slowest you can get (with a load of 255) is 256 ticks of the prescaled clock. If you have an 8 MHz clock and want a timer interval of one msec, you can set the prescaler for 1/32 to get a counter clock of 250000 Hz, then load OCR2A with 249 to get a division by 250 for a 1000 Hz interrupt rate. The Setup code looks like this:

TCCR2A = 2;            // Set CTC mode.  Same as TCCR2A = _BV(WGM21);  
TCCR2B = 3;            // Prescaler to divide by 32 (CS21 and CS20 only)
TCNT2 = 0;             // Clear the counter
OCR2A = 249;           // Set for 1 msec rate
TIMSK2 = 2;            // Set OCIE2A to begin counting with Compare A

Your interrupt handler is declared like this, which should appear after Setup and before Loop:

ISR(TIMER2_COMPA_vect)
{
// Your code goes here
}

Note that the timer can be set up in your main Loop on command from Serial if needed, such as if you don't want to start the interrupts until you have some other needed data. Or you can leave all the setup as-is except for the final TIMSK2 = 2; which can be given by your serial command,