Even here, bits 1 and 0 are allotted for TIMER0. This is also a register shared by all the timers. Setting this bit to ‘1’ enables the TIMER0 overflow interrupt. Right now, we are interested in the 0th bit TOIE0. It is a common register for all the three timers. The Timer/Counter Interrupt Mask – TIMSK Register is as follows. For this, you should be aware of the following registers.
Codevisionavr assembly how to#
Not until you learn how to enable the interrupt feature.
Codevisionavr assembly code#
Please note that the code is not yet ready. Tot_overflow = 0 // reset overflow counter Moving to the coding part, we simply change the initialize function and the compare value. Have a look at the selection highlighted in grey. Now refer to the descriptions of clock select bits as shown in the TCCR0 register. See previous tutorial for details.įrom the values of the counter, we can easily rule out the top three prescalers as they are above the maximum limit of an 8-bit counter (which is 255). Now the following table summarizes the results of using different prescalers 8, 64, 2. So what do we do? Yes, you guessed right (I hope so ))! We use a prescaler in order to trade duration with resolution. Now since the CPU clock frequency is 16 MHz, the maximum time delay that it can measure is 16 μs! But 8 ms (which is quite a small duration for us) is way much larger. Well, 8 ms is still low, but it’s good enough for the following illustration. We need to flash an LED every 8 ms and we have an XTAL of 16 MHz. Now let’s change the above problem statement to the following. Thus to remain on the safer side, we use ‘>=’ instead of ‘=’. This is because sometimes due to missed compares or unexpected increment, this condition may never be true. Thus, we initialize the counter as: TCCR0 |= (1 We will be using it later in this tutorial. The Timer/Counter Register – TCNT0 is as follows:įor this problem statement, we choose No Prescaling. For this, we need the help of the following registers. As soon as it reaches 191, we toggle the LED value and reset the counter. We need to keep a track of the counter value. Thus, what we need to do is quite simple. This can easily be achieved with an 8-bit counter (MAX = 255). Hence for a delay of 6 ms, we need a timer count of 191. This is quite low (for us, but not for the MCU). Now, as per the following formula, with a clock frequency of 32 kHz and 8-bit counter, the maximum delay possible is of 8 ms. Well, I know that an LED flashing at every 6 ms will be always visible as on by our eye, but I could not find any simpler example which does not include prescalers. Let’s say, we need to flash an LED every 6 ms and we are have a CPU clock frequency of 32 kHz. To have an idea about AVR Peripherals, view this page (you need to scroll down a bit). For those who are new to the term ‘register’, they can read about it from this page. Instead of discussing all the registers at once, we will be discussing them as and when necessary. Since timer is a peripheral, it can be activated by setting some bits in some registers. In this tutorial, we will learn to use TIMER0. I have assumed that you have understood the concepts discussed above. So, I will move towards its implementation directly.