Rainbow Electronics ATmega161L - Manual (Page 26)

26
ATmega161(L)
1228C–AVR–08/02
Note: 1. The Power-on Reset will not work unless the supply voltage has been below V
POT
(falling).
‘
Notes: 1. The CKSEL fuses control only the start-up time. The Oscillator is the same for all
selections. On Power-up, the real-time part of the start-up time is increased with typ.
0.6 ms.
2. External Power-on Reset.
3. Table 4 shows the Start-up Times from Reset. From sleep, 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. The number WDT Oscillator cycles used for each time-
out is shown in Table 5.
The frequency of the Watchdog Oscillator is voltage-dependent as shown in the Electri-
cal Characteristics section. The device is shipped with CKSEL = 010.
Table 3. Reset Characteristics (V
CC
= 5.0V) (1)
Symbol Parameter Min Typ Max Units
V
POT
Power-on Reset Threshold Voltage (rising) 1.0 1.4 1.8 V
Power-on Reset Threshold Voltage (falling) (1) 0.4 0.6 0.8 V
V
RST
RESET Pin Threshold Voltage 0.85 V
CC
V
Table 4. Reset Delay Selections (3)
CKSEL
[2:0] Start-up Time, V
CC
= 2.7V,
SUT Unprogrammed
Start-up Time, V
CC
= 4.0V,
SUT Programmed
Recommended
Usage
(1)
000 4.2 ms + 6 CK 5.8 ms + 6 CK External Clock, Fast
Rising Power
001 30 µs + 6 CK 10 µs + 6 CK External Clock (2)
010 67 ms + 16K CK 92 ms + 16K CK Crystal Oscillator,
Slowly Rising
Power
011 4.2 ms + 16K CK 5.8 ms + 16K CK Crystal Oscillator,
Fast Rising Power
100 30 µs + 16K CK 10 µs + 16K CK Crystal Oscillator (2)
101 67 ms + 1K CK 92 ms + 1K CK Ceramic
Resonator/External
Clock, Slowly Rising
Power
110 4.2 ms + 1K CK 5.8 ms + 1K CK Ceramic Resonator,
Fast Rising Power
111 30 µs + 1K CK 10 µs + 1K CK Ceramic
Resonator
(2)
Table 5. Number of Watchdog Oscillator Cycles
SUT Time-out Number of Cycles
Unprogrammed 4.2 ms (at V
CC
= 2.7V) 1K
Unprogrammed 67 ms (at V
CC
= 2.7V) 16K
Programmed 5.8 ms (at V
CC
= 4.0V) 4K
Programmed 92 ms (at V
CC
= 4.0V) 64K