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How often does the ATmega328P wake up from sleep?
R1 can be as low as 220Ω giving a very short pulse and an interrupt is still created. For the tests I wrote a simple sketch with interrupt handling. The ATmega328P running at internal 8MHz clock is in sleep mode most of the time. The controller wakes up once a second by external interrupt 0 fired by a DS1337.
How many interrupts can be generated by ATmega328P?
R1 can vary from 220Ω to 10kΩ to produce one single interrupt with the given short interrupt handling. A value of 2.2kΩ is chosen that should fit for most cases. Then only one interrupt is generated no matter how long the original signal will last after the interrupt is started.
When is there too long a signal no interrupt is detected?
When the signal is too short no interrupt is detected. When too long more than one interrupt is created by one single pulse on the interrupt line. Now let’s go back to our RTC: We will use the square wave output of the RTC with a frequency on 1Hz generating an interrupt once a second.
How are external interrupts triggered on an ATmega328P?
External Interrupts are triggered by the INT0 and INT1 pins or any of the PCINT23..0 pins 23 Pin Change Interrupts are mapped to the 23 General Purpose I/O Port Pins: The INT0 and INT1 interrupts can be triggered by a low logic level, logic change, and a falling or rising edge.
Where is the eifr Register in ATmega328P?
The EIFR register is within the I/O address range (0x00 to 0x1F) of the Set Bit in I/O Register (SBI) Instruction. This flag is always cleared when INT0 is configured as a level interrupt. When Will External Interrupts be Triggered?
What should the R2 value be on ATmega328P?
A high value for R2 ensures that the output voltage really rises almost up to Vcc and minimizes additional loss by the current through R1 + R2 during on-time of Q1. Tests have shown that C1 should not be smaller than 4.7nF to have the output voltage really go to LOW level. On the left you can see the pulse that triggers the interrupt.