![]() It’s value is compared with the Output Compare Register (in CTC mode), and an interrupt is generated when the values match. This register is where the actual counting happens. The CS00, CS01 and CS02 bits of TCCR0B are used to set the prescaler of the clock. This gives you more control on the time interval. In the CTC (Clear Timer on Compare) mode, the interrupt is generated when the value of the counter reaches the value set in OCRA register. If you have an 8-bit counter, you set its value to 0, wait it to reach 0xFF (0xFFFF for 16 bit) and then the interrupt is generated. In normal more, you don’t care about the exact time interval. Generally, one of Normal or CTC modes is used. The TCCR0A register (primarily the WGM00 and WGM01 bits, along with WGM02 bit from TCRR0B register), control the counting sequence of the counter. If you are using Timer0, you will be concerned with TCCR0A and TCCR0B registers. You can find the datasheet here − TCCRxA and TCCRxB We will also provide the page numbers of the ATmega328 (used in Arduino Uno) datasheet wherein you can find detailed information on these registers. In this article, we will just introduce the registers relevant to timer operations and explain their significance. But what if we wish to generate timer interrupts without a third-party library? In that case, you will directly have to meddle with the timer registers in Arduino. For example, timer2 does not have the option of 1024 prescaler.In a previous article, we used the TimerOne library to add timer interrupts to Arduino. Notice in the last step that there are different prescaling options for the different timers. TCCR1B |= (1 << CS11) // Set CS#1 bit for 8 prescaler for timer 1 TCCR2B |= (1 << CS22) // Set CS#2 bit for 64 prescaler for timer 2 This follows directly from the datasheet of the ATMEL 328/168.įinally, notice how the setup for the prescalers follows the tables in the last step (the table for timer 0 is repeated above), ![]() ![]() Remember that when you use timers 0 and 2 this number must be less than 256, and less than 65536 for timer1Īlso notice how the setups between the three timers differ slightly in the line which turns on CTC mode: As explained in the last step, this was calculated according to the following equation:Ĭompare match register = - 1 Notice how the value of OCR#A (the compare match value) changes for each of these timer setups. set compare match register for 8khz increments TCNT2 = 0 //initialize counter value to 0 TCCR2A = 0 // set entire TCCR2A register to 0 Set CS10 and CS12 bits for 1024 prescaler set compare match register for 1hz increments TCNT1 = 0 //initialize counter value to 0 TCCR1A = 0 // set entire TCCR1A register to 0 Set CS01 and CS00 bits for 64 prescaler set compare match register for 2khz increments TCNT0 = 0 //initialize counter value to 0 TCCR0A = 0 // set entire TCCR0A register to 0 The main structure of the interrupt setup looks like this: I pretty much just copy the same main chunk of code and change the prescaler and compare match register to set the correct interrupt frequency. The code involved for setting up timer interrupts is a little daunting to look at, but it's actually not that hard. ![]() Normally when you write an Arduino sketch the Arduino performs all the commands encapsulated in the loop() function in an Arduino sketch. Jump straight to step 2 if you are looking for sample code. In this instructable I'll explain how to setup and execute an interrupt in Clear Timer on Compare Match or CTC Mode. Timer interrupts allow you to perform a task at very specifically timed intervals regardless of what else is going on in your code.
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