Rainbow Electronics Atmega169L - Manual (Page 39)

39
ATmega169V/L
2514A–AVR–08/02
External Reset An External Reset is generated by a low level on the RESET pin. Reset pulses longer
than the minimum pulse width (see Table 16) will generate a reset, even if the clock is
not running. Shorter pulses are not guaranteed to generate a reset. When the applied
signal reaches the Reset Threshold Voltage – V
RST
– on its positive edge, the delay
counter starts the MCU after the Time-out period – t
TOUT
– has expired.
Figure 17. External Reset During Operation
Brown-out Detection ATmega169 has an On-chip Brown-out Detection (BOD) circuit for monitoring the V
CC
level during operation by comparing it to a fixed trigger level. The trigger level for the
BOD can be selected by the BODLEVEL Fuses. The trigger level has a hysteresis to
ensure spike free Brown-out Detection. The hysteresis on the detection level should be
interpreted as V
BOT+
= V
BOT
+ V
HYST
/2 and V
BOT-
= V
BOT
- V
HYST
/2.
Note: 1. 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 = 110 for ATmega169V and
BODLEVEL = 101 for ATmega169L.
CC
Table 17. BODLEVEL Fuse Coding (1)
BODLEVEL 2..0 Fuses Min V
BOT
Typ V
BOT
Max V
BOT
Units
111 BOD Disabled
110 1.8
V 101 2.7
100 4.3
011
Reserved
010
001
000
Table 18. Brown-out Characteristics
Symbol Parameter Min Typ Max Units
V
HYST
Brown-out Detector Hysteresis 50 mV
t
BOD
Min Pulse Width on Brown-out Reset ns