Rainbow Electronics ATmega64L - Manual (Page 25)

25
ATmega16(L)
2466B–09/01
The CKSEL0 fuse together with the SUT1..0 fuses select the start-up times as shown in
Table 5.
Notes: 1. These options should only be used when not operating close to the maximum fre-
quency of the device, and only if frequency stability at start-up is not important for the
application. These options are not suitable for crystals.
2. These options are intended for use with ceramic resonators and will ensure fre-
quency stability at start-up. They can also be used with crystals when not operating
close to the maximum frequency of the device, and if frequency stability at start-up is
not important for the application.
Low-frequency Crystal
Oscillator To use a 32.768 kHz watch crystal as the clock source for the device, the low-frequency
crystal oscillator must be selected by setting the CKSEL fuses to “1001”. The crystal
should be connected as shown in Figure 12. By programming the CKOPT fuse, the user
can enable internal capacitors on XTAL1 and XTAL2, thereby removing the need for
external capacitors. The internal capacitors have a nominal value of 36 pF. Refer to the
32 kHz Crystal Oscillator application note for details on oscillator operation and how to
choose appropriate values for C1 and C2.
Table 5. Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0 SUT1..0
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
(V
CC
= 5.0V) Recommended Usage
0 00 258 CK (1) 4 ms
Ceramic resonator, fast
rising power
0 01 258 CK (1) 64 ms
Ceramic resonator, slowly
rising power
0 10 1K CK (2) –
Ceramic resonator, BOD
enabled
0 11 1K CK (2) 4 ms
Ceramic resonator, fast
rising power
1 00 1K CK (2) 64 ms
Ceramic resonator, slowly
rising power
1 01 16K CK –
Crystal oscillator, BOD
enabled
1 10 16K CK 4 ms
Crystal oscillator, fast
rising power
1 11 16K CK 64 ms
Crystal oscillator, slowly
rising power