Datasheet

36
8272A–AVR–01/10
164A/164PA/324A/324PA/644A/644PA/1284/1284P
Ce - is optional external capacitors as described in Figure 8-2 on page 32
Ci - is is the pin capacitance in Table 8-8 on page 35
CL - is the load capacitance for a 32.768 kHz crystal specified by the crystal vendor.
C
S
- is the total stray capacitance for one TOSC pin.
Crystals specifying load capacitance (CL) higher than the ones given in the Table 8-8 on page
35, require external capacitors applied as described in Figure 8-2 on page 32.
Figure 8-3. Crystal Oscillator Connections
Crystals specifying load capacitance (CL) higher than listed in Table 8-8 on page 35, require
external capacitors applied as described in Figure 8-2 on page 32.
To find suitable load capacitance for a 32.768 kHz crysal, please consult the crystal datasheet.
When this oscillator is selected, start-up times are determined by the SUT Fuses and CKSEL0
as shown in Table 8-9.
Note: 1. These options should only be used if frequency stability at start-up is not important for the
application.
Table 8-9. Start-up Times for the Low Frequency Crystal Oscillator Clock Selection
Power Conditions
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
(V
CC
= 5.0V) CKSEL0 SUT1..0
BOD enabled 1K CK 14CK
(1)
000
Fast rising power 1K CK 14CK + 4.1 ms
(1)
001
Slowly rising power 1K CK 14CK + 65 ms
(1)
010
Reserved 0 11
BOD enabled 32K CK 14CK 1 00
Fast rising power 32K CK 14CK + 4.1 ms 1 01
Slowly rising power 32K CK 14CK + 65 ms 1 10
Reserved 1 11