Also, you should spell and capitalize them correctly (see here). The general guidelines on ISRs are to make them as short as possible and not use delays in them. The last step is to write the ISR that will be called for each of these interrupts. PCMSK1 |= 0b00010000 // turn on pin PC4, which is PCINT12, physical pin 27 PCMSK0 |= 0b00000001 // turn on pin PB0, which is PCINT0, physical pin 14 Again, you can use |= or just = but |= gives you the ability to separate them onto different lines if you’d like. These are set the same way the register for the PCICR was set. Since the ATMEGA328 has 3 ports, it also has three masks: PCMSK0, PCMSK1, and PCMSK2. I know I said earlier that a change on any of the pins in a port would trigger the port’s ISR, but that is true only when you turn that particular pin on. You can also use decimal or hexadecimal instead of binary, but I think the binary is the easiest to understand. Note, I’m using |= instead of = because it is more versatile but either would work. This code shows how to turn them on or off. Bit 0 turns on port B (PCINT0 – PCINT7), bit 1 turns on port C (PCINT8 – PCINT14), and bit 2 turns on port D (PCINT16 – PCINT23). The Pin Change Interrupts are turned on by setting certain bits in the PCICR register as seen below. There are three steps to using Pin Change Interrupts. For these reasons, all of the below will use AVR C commands, which can be used regardless of whether you’re using the Arduino boot-loader and IDE or another. I just feel like it’s easier to debug and control what’s going on. Plus, I’m a fan of not using libraries for simple tasks like this that could be accomplished in a few lines of code. But up until recently, there wasn’t a good Pin Change Interrupt library and even now it isn’t included so you have to download it separately. You just call the function attachInterrupt and input the interrupt number and the function to call when it triggers. Hardware interrupts are also easier to use in the Arduino environment. So Pin Change Interrupts are harder to use but you get the benefit of being about to use any pin. And anytime a pin changes on that port, it calls the port’s ISR which must then decide which pin caused the interrupt. But the Pin Change Interrupts share an ISR between all the pins on a port (port B, C, and D). Each External Interrupt has its own ISR and they can be triggered independently by either a rising signal, falling signal, or by both. For instance, on the ATMEGA328, there are two External Interrupts but 24 Pin Change Interrupts.Įach time an interrupt occurs, it triggers the associated ISR (Interrupt Service Routine) assuming you have turned that interrupt on. But the things we are now calling External Interrupts are limited to only a couple pins, while the Pin Change interrupts can occur on all input pins. The nomenclature here is confusing since all hardware interrupts are external to the chip. Within the Hardware interrupt there are two categories: External interrupts and Pin Change Interrupts. A Hardware interrupt is triggered by something outside of the chip like a button while a Software interrupt is triggered from inside the chip like a timer. There are two main categories of interrupts: Hardware and Software. Before we begin I want to make sure we’re all using the same terms. I’m going to talk specifically about the ATMEGA328 chip here since it is by far the most common in Arduinos and in my lab, but the information here should transfer easily other ATMEGAs as well. I’m posting this so that when I need to look it up in the future, I can easily find it and maybe I can help somebody else out too. As it turns out, they’re actually pretty easy. I recently needed to do some work with Pin Change Interrupts and it was a bit of a learning experience for me.
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