Rainbow Electronics ATmega163L - Manual (Page 23)

ATmega163(L)
23
Notes: 1. On power-up, the start-up time is increased with typ. 0.6 ms.
2. ‘1’ means unprogrammed, ‘0’ means programmed.
3. For possible clock selections, see “Clock Options” on page 5.
4. When BODEN is programmed, add 100 µs.
5. When BODEN is programmed, add 25 µs.
6. Default value.
Table 5 shows the start-up times from reset. When the CPU wakes up from power down or power save, 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 of WDT oscillator cycles used for each time-out is shown in Table 6.
The frequency of the watchdog oscillator is voltage dependent as shown in the Electrical Characteristics section. The
device is shipped with CKSEL = ‘0010’ (Int. RC Oscillator, slowly rising power).
Note: The bod-level fuse can be used to select start-up times even if the Brown-out detection is disabled (BODEN fuse
unprogrammed).
Power-on Reset
A Power-on Reset (POR) pulse is generated by an on-chip detection circuit. The detection level is defined in Table 4. 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 to detect a failure in supply voltage.
A 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 5. The RESET signal is activated again, without any delay, when the V
CC
decreases
below detection level.
0111 30 µs + 6 CK (4) 10 µs + 6 CK (5) Ext. RC Oscillator, BOD enabled
1000 67ms + 32K CK 92 ms + 32K CK Ext. Low-frequency Crystal
1001 67 ms + 1K CK 92 ms + 1K CK Ext. Low-frequency Crystal
1010 67 ms + 16K CK 92 ms + 16K CK Crystal Oscillator, slowly rising power
1011 4.2 ms + 16K CK 5.8 ms + 16K CK Crystal Oscillator, fast rising power
1100 30 µs + 16K CK (4) 10 µs + 16K CK (5) Crystal Oscillator, BOD enabled
1101 67 ms + 1K CK 92 ms + 1K CK Ceramic Resonator/Ext. Clock, slowly rising power
1110 4.2 ms + 1K CK 5.8 ms + 1K CK Ceramic Resonator, fast rising power
1111 30 µs + 1K CK (4) 10 µs + 1K CK (5) Ceramic Resonator, BOD enabled
Table 6. Number of Watchdog Oscillator Cycles
BODLEVEL V
cc
condition Time-out Number of cycles
Unprogrammed 2.7V 30 µs 8
Unprogrammed 2.7V 130 µs 32
Unprogrammed 2.7V 4.2 ms 1K
Unprogrammed 2.7V 67 ms 16K
Programmed 4.0V 10 µs 8
Programmed 4.0V 35 µs 32
Programmed 4.0V 5.8 ms 4K
Programmed 4.0V 92 ms 64K
Table 5. Reset Delay Selections (1) (Continued)
CKSEL (2)
Start-up Time, V
CC
= 2.7V,
BODLEVEL Unprogrammed
Start-up Time, V
CC
= 4.0V,
BODLEVEL Programmed Recommended Usage (3)