46
8126F–AVR–05/12
ATtiny13A
9.2
External Interrupts
The External Interrupts are triggered by the INT0 pin or any of the PCINT[5:0] pins. Observe
that, if enabled, the interrupts will trigger even if the INT0 or PCINT[5:0] pins are configured as
outputs. This feature provides a way of generating a software interrupt. Pin change interrupts
PCI will trigger if any enabled PCINT[5:0] pin toggles. The PCMSK Register control which pins
contribute to the pin change interrupts. Pin change interrupts on PCINT[5:0] 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 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 MCU Control Register – MCUCR. 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 Systems and their Distribution” on page 23
.
9.2.1
Low Level Interrupt
A 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 inter-
rupt 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 23
If the low level on the interrupt pin is removed before the device has woken up then program
execution will not be diverted to the interrupt service routine but continue from the instruction fol-
lowing the SLEEP command.
9.2.2
Pin Change Interrupt Timing
An example of timing of a pin change interrupt is shown in
below.
Figure 9-1.
Timing of pin change interrupts
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