55
ATmega16M1/32M1/64M1 [DATASHEET]
8209E–AVR–11/2012
12. External interrupts
The External Interrupts are triggered by the INT3:0 pins or any of the PCINT23:0 pins. Observe that, if enabled, the
interrupts will trigger even if the INT3:0 or PCINT23:0 pins are configured as outputs. This feature provides a way
of generating a software interrupt. The pin change interrupt PCI2 will trigger if any enabled PCINT23:16 pin tog-
gles. The pin change interrupt PCI1 will trigger if any enabled PCINT14:8 pin toggles. The pin change interrupt
PCI0 will trigger if any enabled PCINT7:0 pin toggles. The PCMSK3, PCMSK2, PCMSK1 and PCMSK0 Registers
control which pins contribute to the pin change interrupts. Pin change interrupts on PCINT26:0 are detected asyn-
chronously. This implies that these interrupts can be used for waking the part also from sleep modes other than
Idle mode.
The INT3:0 interrupts can be triggered by a falling or rising edge or a low level. This is set up as indicated in the
specification for the External Interrupt Control Register A – EICRA. When the INT3:0 interrupts are enabled and
are configured as level triggered, the interrupts will trigger as long as the pin is held low. Note that recognition of
falling or rising edge interrupts on INT3:0 requires the presence of an I/O clock, described in
“Clock systems andrupt can be used for waking the part also from sleep modes other than Idle mode. The I/O clock is halted in all
sleep modes except Idle mode.
Note that if a level triggered interrupt is used for wake-up from Power-down, the required level must be held long
enough for the MCU to complete the wake-up to trigger the level interrupt. If the level disappears before the end of
the Start-up Time, the MCU will still wake up, but no interrupt will be generated. The start-up time is defined by the
12.1
Pin change interrupt timing
An example of timing of a pin change interrupt is schown in
Figure 12-1.Figure 12-1. Timing of a pin change interrupts.
LE
DQ
clk
pin_lat
pin_sync
pcint_in[i]
PCINT[i]
pin
PCINT[i] bit
(of PCMSKn)
DQ
clk
pcint_sync
pcint_set/flag
0
7
PCIFn
(interrupt
flag)
PCINT[i] pin
pin_lat
pin_sync
clk
pcint_in[i]
pcint_syn
pcint_set/flag
PCIFn