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AT90S8414
Preliminary
4-33
enters the interrupt routine and resumes execution from the address following the last executed instruction. To avoid
entering the Interrupt Routine, let a CLI - Disable Global Interrupts follow the SLEEP instruction. If reset occurs while
the MCU is in Sleep Mode, the MCU awakes and executes from the reset vector. The contents of the register file and the
I/O memory are unaltered in both modes.
Note that if a level triggered interrupt is used for wake-up, the low level must be held for a time longer than the oscillator
start-up time of 16 ms. Otherwise, the interrupt flag may return to zero before the MCU starts executing.
IDLE MODE
When the SM bit is cleared (zero), the SLEEP instruction forces the MCU into the Idle Mode stopping the CPU but
allowing Timer/Counters, Watchdog and the interrupt system to continue operating. This enables the MCU to wake up
from external triggered interrupts as well as internal ones like Timer Overflow interrupt and watchdog reset. If wakeup
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 during Idle
Mode.
POWER DOWN MODE
When the SM bit is set (one), the SLEEP instruction forces the MCU into the Power Down Mode. In this mode, the
oscillator is stopped. The user can select whether the watchdog shall be enabled during power-down mode. If the
watchdog is enabled, it will wake up the MCU when the Watchdog Time-out period expires. If the watchdog is disabled,
only an external reset or an external interrupt can wake up the MCU.
Timer / Counters
The AT90S8414 provides two general purpose Timer/Counters - one 8-bit T/C and one 16-bit T/C. The Timer/Counters
have separate prescaling selection from the same 10-bit prescaling timer. Both Timer/Counters can either be used as a
timer with an internal clock timebase or as a counter with an external pin connection which triggers the counting.
The Timer/Counter Prescaler
Figure 31 shows the general Timer/Counter prescaler.
Figure 31: Timer/Counter Prescaler