ATTINY85 / external inerrupt INT0 / RISING

I’m trying for days to get ATTINY85 external interrupt on rising edge working. I’ve looked around very extendly and read the datsheet carefully. But the code doesn’t work. Here it is:

#include <avr/sleep.h>
#include <avr/wdt.h>

/* macros

  • sbi(): a macro to set the bit(the second argument) of the address(the first argument) to 1.
    #ifndef cbi
    #define cbi(sfr, bit) (_SFR_BYTE(sfr) &= -_BV(bit))
    #ifndef sbi
    #define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))

volatile int i, i1;
volatile int wakePin = 2; // choose input pin (for PIR sensor) INT0, PCINT2 (PB2) / IC-Pin 7
volatile int ledPin = 4; // choose the pin for the LED (PB4) / IC-Pin 3


  • here the interrupt is handled after wakeup
    ISR(INT0_vect) {
    for (int i = 0; i < 6; i++){ // ISR-handler information on led
    digitalWrite(ledPin, HIGH);
    digitalWrite(ledPin, LOW);
    cli(); // disable interrupts
    cbi(GIMSK,INT0); // turns off INT0 as interrupt pin
    sleep_disable(); // clear sleep enable bit

volatile void system_sleep() {
sbi(GIMSK,INT0); // Changes Interrupt to PB2 (PCINT2 / INT0)
sbi(MCUCR, ISC01);
sbi(MCUCR, ISC00);

set_sleep_mode(SLEEP_MODE_PWR_DOWN); // sleep mode is set here
sleep_enable(); // sets the Sleep Enable bit in the MCUCR Register (SE BIT)
sei(); // enable interrupts
sleep_mode(); // sleep begins here, the device is actually put to sleep!!

void setup() {
pinMode(wakePin, INPUT); // declare sensor as input
pinMode(ledPin, OUTPUT);
for (int i = 0; i < 3; i++){ // setup information on led
digitalWrite(ledPin, HIGH);
digitalWrite(ledPin, LOW);

void loop(){
digitalWrite(ledPin, HIGH);
delay (1000);
digitalWrite(ledPin, LOW);
system_sleep(); // Runs the system_sleep() function

It bases mainly on this example . There is a resistor between GND and PIN 7. If I set PIN 7 to HIGH nothing happens. IF I set only ISC01 nothing happens, neither with the resistor on GND and setting Pin7 to HIGH nor resistor on VCC and setting Pin7 to LOW. Same with ISC00 ist setted and ISC01 not.
The only workink constalation is ISC00 = LOW and ISC01 = LOW. But I need the RISING option.

Than for helpis

I’m curious to see how far you get with this. I had exactly the same problem with an ATTINY84 recently (getting it to wake up on being triggered by a PIR) and had to change my code to wake up on a pin change interrupt instead of an external interrupt, and that works perfectly well.

On reading the data sheet very carefully, I came to the conclusion that it would work for INT0 waking up only on a level change and not an edge trigger. That level can only be LOW on an ATTINY85.


In Chapter 9.2 External Interrupts, there appears to be a distinction between level and edge triggering:

. . .
The INT0 interrupts can be triggered by a falling or rising edge or a low level.
. . .

This also makes it clearer, again from the datasheet Ch 9.2:

Note that recognition of falling or rising edge
interrupts on INT0 requires the presence of an I/O clock

The clock is not running in this sleep mode.

I have seen examples ( sketch J ) for the ATMEGA328P where it wakes up OK on an edge trigger and the data sheet has more or less the same wording, so there is also clearly something that I do not understand.

By the way, your link above does not work.

aahhhh, thank you! I've got it now. Yes, that's it. The exact link is example (hope it works now) Thank you again.

6v6gt: I have seen examples ( sketch J ) for the ATMEGA328P where it wakes up OK on an edge trigger and the data sheet has more or less the same wording, so there is also clearly something that I do not understand.

This is more than a year old thread, but I will comment this in case somebody encounters this later. The datasheet are wrong on that part in the table. Nick Gammon confirmed that in 2015 from Atmel staff: Every type of interrupt (both edge and level) will wake up the AVR from sleep. I've confirmed this in hardware on at least attiny10 & atmega328p. And I think this is the same for every other AVR MCU with same type of INTx interrupt(s). The Microchip should really fix this at once.

OK but this thread was about this behaviour on an ATTINY85. This (triggering of external interrupts in sleep mode) is exactly where there is a difference between the ATMEGA and ATTINY. It looks like there has been a cut and paste error between the data sheets. Yes it works on an ATMEGA328P but [u]not[/u] on an ATTINY85.

This topic appears here from time to time

Keywords for searches:

ATTINY edge triggered interrupt fails to wakeup ATMEGA can wakeup on rising edge interrupt ATMEGA datasheet error external interrupts sleep mode AVR wakeup by external interrupt

Well at least not every attiny are affected (by not waking up). I can confirm that attiny10 does wakes up on falling edge INT0 interrupt. Tested in hardware.