Rainbow Electronics ATtiny26L - Manual (Page 22)

22
ATtiny26(L)
1477B–AVR–04/02
0
Notes: 1. The Power-on Reset will not work unless the supply voltage has been below V
POT
(falling)
2. V
BOT
may be below nominal minimum operating voltage for some devices. For
devices where this is the case, the device is tested down to V
CC
= V
BOT
during the
production test. This guarantees that a Brown-out Reset will occur before V
CC
drops
to a voltage where correct operation of the microcontroller is no longer guaranteed.
The test is performed using BODLEVEL=1 for ATtiny26L and BODLEVEL=0 for
ATtiny26. BODLEVEL=1 is not applicable for ATtiny26.
See start-up times from reset from “System Clock and Clock Options” on page 25.
When the CPU wakes up from Power-down, only the clock counting part of the start-up
time is used. The Watchdog Oscillator is used for timing the real-time part of the start-up
time.
Power-on Reset A Power-on Reset (POR) pulse is generated by an On-chip Detection circuit. The detec-
tion level is defined in Table 3 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 deter-
mines 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 “System Clock and Clock
Options” on page 25. The RESET signal is activated again, without any delay, when the
V
CC
decreases below detection level.
Table 3. Reset Characteristics
Symbol Parameter Condition Min Typ Max Units
V
POT
Power-on Reset Threshold
Voltage (rising)
1.4 2.3 V
Power-on Reset Threshold
Voltage (falling)
(1)
1.3 2.3 V
V
RST
RESET Pin Threshold Voltage 0.1 0.9 V
CC
t
RST
Minimum pulse width on
RESET Pin
50 ns
V
BOT
Brown-out Reset Threshold
Voltage
(2)
BODLEVEL = 1 2.5 2.7 3.2
V
BODLEVEL = 0 3.7 4.0 4.2
t
BOD
Minimum low voltage period for
Brown-out Detection BODLEVEL = 1 2 µs
BODLEVEL = 0 2 µs
V
HYST
Brown-out Detector hysteresis 130 mV