ATtiny10/11/12
20
The frequency of the watchdog oscillator is voltage dependent as shown in the section “ATtiny11 Typical Characteristics”
on page 54.
Note that the BODLEVEL fuse can be used to select start-up times even if the Brown-out Detection is disabled (by leaving
the BODEN fuse unprogrammed).
The device is shipped with CKSEL3..0 = 0010.
Power-on Reset for the ATtiny12
A Power-on Reset (POR) pulse is generated by an on-chip detection circuit. The detection level is nominally 1.4V. The
POR is activated whenever V
CC
is below the detection level. The POR circuit can be used to trigger the start-up reset, as
well as detect a failure in supply voltage.
The Power-on Reset (POR) circuit ensures that the device is reset from power-on. Reaching the Power-on Reset threshold
voltage invokes a delay counter, which determines the delay for which the device is kept in Reset after V
CC
rise. The time-
out period of the delay counter can be defined by the user through the CKSEL fuses. The different selections for the delay
period are presented in Table 9. The Reset signal is activated again, without any delay, when the V
CC
decreases below
detection level.
If the built-in start-up delay is sufficient, RESET can be connected to V
CC
directly or via an external pull-up resistor. See
Figure 18. By holding the RESET pin low for a period after V
CC
has been applied, the Power-on Reset period can be
extended. Refer to Figure 19 for a timing example on this.
Figure 18. MCU Start-up, RESET Tied to V
CC
.
Table 10. Number of Watchdog Oscillator Cycles
BODLEVEL
Time-out
Number of Cycles
Unprogrammed
3.6 ms (at V
cc
= 1.8V)
256
Unprogrammed
57 ms (at V
cc
= 1.8V)
4K
Programmed
4.2 ms (at V
cc
= 2.7V)
1K
Programmed
67 ms (at V
cc
= 2.7V)
16K
V
CC
RESET
TIME-OUT
INTERNAL
RESET
t
TOUT
V
POT
V
RST
