AT89LP216_09 Datasheet, PDF (17/98 Pages) ATMEL Corporation – 8-bit Microcontroller with 2K Bytes Flash

Figure 11-1. Interrupt Recovery from Power-down (PWDEX = 0)
PWD
XTAL1
tSUT
INT1
Internal
Clock
AT89LP216
When PWDEX = “1”, the wake-up period is controlled externally by the interrupt. Again, at the
falling edge on the interrupt pin, power-down is exited and the oscillator is restarted. However,
the internal clock will not propagate until the rising edge of the interrupt pin as shown in Figure
11-2. The interrupt pin should be held low long enough for the selected clock source to stabilize.
After the rising edge on the pin the interrupt service routine will be executed.
Figure 11-2. Interrupt Recovery from Power-down (PWDEX = 1)
PWD
XTAL1
INT1
Internal
Clock
11.2.2
Reset Recovery from Power-down
The wake-up from Power-down through an external reset is similar to the interrupt with
PWDEX = “0”. At the falling edge of RST, Power-down is exited, the oscillator is restarted, and
an internal timer begins counting as shown in Figure 11-3. The internal clock will not be allowed
to propagate to the CPU until after the timer has timed out. The time-out period is controlled by
the Start-up Timer Fuses. (See Table 10-1 on page 15). If RST returns high before the time-out,
a two clock cycle internal reset is generated when the internal clock restarts. Otherwise the
device will remain in reset until RST is brought high.
Figure 11-3. Reset Recovery from Power-down.
PWD
XTAL1
tSUT
RST
Internal
Clock
Internal
Reset
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