ATtiny261A datasheet(50/292 Pages) ATMEL

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8197A–AVR–10/09

ATtiny261A/461A/861A

9.2.1

Low Level Interrupt

A low level interrupt on INT0 is detected asynchronously. This means that the interrupt source

can be used for waking the part also from sleep modes other than Idle (the I/O clock is halted in

all sleep modes except Idle).

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 “Clock System” on page 24.

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.

9.3

9.3.1

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 9-2. 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.

9.3.2

GIMSK – General Interrupt Mask Register

• Bit 7 – INT1: External Interrupt Request 1 Enable

When the INT1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the exter-

nal pin interrupt is enabled. The Interrupt Sense Control0 bits 1/0 (ISC01 and ISC00) in the MCU

Bit

7654

0x35 (0x55)

BODS

PUD

SM1

SM0

BODSE

ISC01

ISC00

MCUCR

Read/Write

R/W

Initial Value

0000

Table 9-2.

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.

Bit

76543

210

0x3B (0x5B)

INT1

INT0

PCIE1

PCIE0

–

–––GIMSK

Read/Write

R/W

R/w

Initial Value

00000

000

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