ATMEGA2561V ATMEL [ATMEL Corporation], ATMEGA2561V Datasheet - Page 77

• Manufacturer Part Number: ATMEGA2561V
• Description: 8-bit Microcontroller with 64K/128K/256K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

External Interrupts
Pin Change Interrupt
Timing
2549K–AVR–01/07
The External Interrupts are triggered by the INT7:0 pin or any of the PCINT23:0 pins.
Observe that, if enabled, the interrupts will trigger even if the INT7:0 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 toggles, Pin
change interrupt PCI1 if any enabled PCINT15:8 toggles and Pin change interrupts
PCI0 will trigger if any enabled PCINT7:0 pin toggles. PCMSK2, PCMSK1 and PCMSK0
Registers control which pins contribute to the pin change interrupts. Pin change inter-
rupts on PCINT23 :0 are detected asynchronously. This implies that these interrupts can
be used for waking the part also from sleep modes other than Idle mode.
The External 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 Registers –
EICRA (INT3:0) and EICRB (INT7:4). When the external interrupt is enabled and is con-
figured 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 INT7:4 requires the presence of an
I/O clock, described in “Overview” on page 37. Low level interrupts and the edge inter-
rupt on INT3:0 are detected asynchronously. This implies that these interrupts 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 37.
An example of timing of a pin change interrupt is shown in Figure 31.
Figure 31. Normal pin change interrupt.
PCINT(0)
pcint_setflag
pcint_in_(n)
clk
PCINT(n)
pcint_syn
pin_sync
pin_lat
PCIF
LE
clk
pin_lat
D
ATmega640/1280/1281/2560/2561
Q
pin_sync
PCINT(0) in PCMSK(x)
pcint_in_(0)
0
x
clk
pcint_syn
pcint_setflag
PCIF
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