ATtiny261-ESSZ datasheet(52/227 Pages) ATMEL

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7753C–AVR–07/09

ATtiny261/ATtiny461/ATtiny861

11. External Interrupts

The External Interrupts are triggered by the INT0 or INT1 pin or any of the PCINT15..0 pins.

Observe that, if enabled, the interrupts will trigger even if the INT0, INT1 or PCINT15..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 PCINT15..0 pin toggles. The PCMSK Register

control which pins contribute to the pin change interrupts. Pin change interrupts on PCINT15..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 INT0 and INT1 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 or INT1 requires

the presence of an I/O clock, described in “Clock Systems 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 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 25.

11.1

11.1.1

MCUCR – MCU Control Register

The MCU Register contains control bits for interrupt sense control.

• Bits 1, 0 – ISC01, ISC00: Interrupt Sense Control 0 Bit 1 and Bit 0

The External Interrupt 0 is activated by the external pin INT0 or INT1 if the SREG I-flag and the

corresponding interrupt mask are set. The level and edges on the external INT0 or INT1 pin that

activate the interrupt are defined in Table 11-1. The value on the INT0 or INT1 pin is sampled

before detecting edges. If edge or toggle interrupt is selected, pulses that last longer than one

clock period will generate an interrupt. Shorter pulses are not guaranteed to generate an inter-

rupt. If low level interrupt is selected, the low level must be held until the completion of the

currently executing instruction to generate an interrupt.

Bit

3210

0x35 (0x55)

–

PUD

SM1

SM0

–

ISC01

ISC00

MCUCR

Read/Write

R/W

R/WR/W

R/WR

R/WR/W

Initial Value

0000

Table 11-1.

Interrupt 0 Sense Control

ISC01

ISC00

Description

The low level of INT0 or INT1 generates an interrupt request.

Any logical change on INT0 or INT1 generates an interrupt request.

The falling edge of INT0 or INT1 generates an interrupt request.

The rising edge of INT0 or INT1 generates an interrupt request.

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