37
ATtiny26(L)
1477G–AVR–03/05
• 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 if the SREG I-flag and the
corresponding interrupt mask is set (one). The activity on the external INT0 pin that acti-
vates the interrupt is defined in the following table.
Note:
1. When changing the ISC10/ISC00 bits, INT0 must be disabled by clearing its Interrupt
Enable bit in the GIMSK Register. Otherwise an interrupt can occur when the bits are
changed.
Idle Mode
When the SM1..0 bits are written to “00”, the SLEEP instruction makes the MCU enter
Idle mod e, stopping the CPU but allo wing Ana lo g Co mpa rator, ADC, USI,
Timer/Counters, Watchdog, and the interrupt system to continue operating. This sleep
mode basically halts clk
CPU
and clk
FLASH
, while allowing the other clocks to run.
Idle mode enables the MCU to wake up from external triggered interrupts as well as
internal ones like the Timer Overflow and USI Start and Overflow interrupts. If wake-up
from the Analog Comparator interrupt is not required, the Analog Comparator can be
powered down by setting the ACD bit in the Analog Comparator Control and Status
Register – ACSR. This will reduce power consumption in Idle mode. If the ADC is
enabled, a conversion starts automatically when this mode is entered.
ADC Noise Reduction
Mode
When the SM1..0 bits are written to “01”, the SLEEP instruction makes the MCU enter
ADC Noise Reduction mode, stopping the CPU but allowing the ADC, the External Inter-
rupts, the USI start condition detection, and the Watchdog to continue operating (if
enabled). This sleep mode basically halts clk
I/O
, clk
CPU
, and clk
FLASH
, while allowing the
other clocks to run.
This improves the noise environment for the ADC, enabling higher resolution measure-
ments. If the ADC is enabled, a conversion starts automatically when this mode is
entered. Apart form the ADC Conversion Complete interrupt, only an External Reset, a
Watchdog Reset, a Brown-out Reset, USI start condition interrupt, an EEPROM ready
interrupt, an External Level Interrupt on INT0, or a pin change interrupt can wake up the
MCU from ADC Noise Reduction mode.
Power-down Mode
When the SM1..0 bits are written to “10”, the SLEEP instruction makes the MCU enter
Power-down mode. In this mode, the External Oscillator is stopped, while the External
Interrupts, the USI start condition detection, and the Watchdog continue operating (if
enabled). Only an External Reset, a Watchdog Reset, a Brown-out Reset, USI start con-
dition interrupt, an External Level Interrupt on INT0, or a pin change interrupt can wake
up the MCU. This sleep mode basically halts all generated clocks, allowing operation of
asynchronous modules only.
When waking up from Power-down mode, there is a delay from the wake-up condition
occurs until the wake-up becomes effective. This allows the clock to restart and become
stable after having been stopped. The wake-up period is defined by the same CKSEL
Fuses that define the reset time-out period, as described in “Clock Sources” on page 24.
Table 18. Interrupt 0 Sense Control
ISC01
ISC00
Description
0
0
The low level of INT0 generates an interrupt request.
0
1
Any change on INT0 generates an interrupt request.
1
0
The falling edge of INT0 generates an interrupt request.
1
1
The rising edge of INT0 generates an interrupt request.
