Rainbow Electronics AT90C8534 - Manual (Page 24)

AT90C8534
24
Power-down Mode
When the SM bit is set (one), the SLEEP instruction makes the MCU enter the Power-down Mode. In this mode, the
external oscillator is stopped, while the external interrupts continue operating. Only an external reset or an external edge
interrupt on INT0 or INT1 can wake up the MCU.
Note that if INT0 or INT1 is used for wake-up from Power-down Mode, the edge is remembered until the MCU wakes up.
When waking up from Power-down Mode, 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 equal to the reset
delay time-out period t
TOUT
.
Timer/Counters
The AT90C8534 provides two general-purpose Timer/Counters – one 8-bit T/C and one 16-bit T/C. Timer/Counters 0 and
1 have individual prescaling selection from the same 10-bit prescaling timer.
Timer/Counter Prescaler
Figure 26. Prescaler for Timer/Counter0 and 1
For Timer/Counters 0 and 1, the five different prescaled selections are: CK, CK/8, CK/64, CK/256 and CK/1024, where CK
is the oscillator clock. In addition, the Timer/Counters can be stopped.
8-bit Timer/Counter0
Figure 27 shows the block diagram for Timer/Counter0.
The 8-bit Timer/Counter0 can select clock source from CK or prescaled CK. In addition, it can be stopped as described in
the specification for the Timer/Counter0 Control Register – TCCR0. The overflow status flag is found in the Timer/Counter
Interrupt Flag Register – TIFR. Control signals are found in the Timer/Counter0 Control Register – TCCR0. The interrupt
enable/disable setting for Timer/Counter0 is found in the Timer/Counter Interrupt Mask Register – TIMSK.
The 8-bit Timer/Counter0 features both a high resolution and a high accuracy usage with the lower prescaling opportuni-
ties. Similarly, the high prescaling opportunities make the Timer/Counter0 useful for lower speed functions or exact timing
functions with infrequent actions.