Rainbow Electronics ATmega3290P_V - Manual (Page 54)

54
ATmega329/3290/649/6490
2552H–AVR–11/06
External Interrupts
The External Interrupts are triggered by the INT0 pin or any of the PCINT30..0 pins.
Observe that, if enabled, the interrupts will trigger even if the INT0 or PCINT30..0 pins
are configured as outputs. This feature provides a way of generating a software inter-
rupt. The pin change interrupt PCI1 will trigger if any enabled PCINT15..8 pin toggles.
Pin change interrupts 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 PCINT30..0 are detected asynchro-
nously. This implies that these interrupts can be used for waking the part also from sleep
modes other than Idle mode.
The INT0 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 INT0 interrupt is enabled and is configured as level triggered, the
interrupt will trigger as long as the pin is held low. Note that recognition of falling or rising
edge interrupts on INT0 requires the presence of an I/O clock, described in “Clock Sys-
tems and their Distribution” on page 25. Low level interrupt on INT0 is detected
asynchronously. This implies that this interrupt 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
SUT and CKSEL Fuses as described in “System Clock and Clock Options” on page 25.
Pin Change Interrupt
Timing An example of timing of a pin change interrupt is shown in Figure 22.
Figure 22. Pin Change Interrupt
clk
PCINT(n)
pin_lat
pin_sync
pcint_in_(n)
pcint_syn
pcint_setflag
PCIF
PCINT(0)
pin_sync
pcint_syn
pin_lat
D Q
LE
pcint_setflag
PCIF
clk
clk
PCINT(0) in PCMSK(x)
pcint_in_(0)
0
x