
35
8018P–AVR–08/10
ATmega169P
The capacitance (Ce + Ci) needed at each TOSC pin can be calculated by using:
where
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, require
The Low-frequency Crystal Oscillator must be selected by setting the CKSEL Fuses to “0110” or
“0111” as shown in
Table 8-10. Start-up times are determined by the SUT Fuses as shown in
Note:
1. This option should only be used if frequency stability at start-up is not important for the
application
Table 8-8.
Capacitance for Low-Frequency Crystal Oscillator
Device
32 kHz Osc. Type
Cap (Xtal1/Tosc1)
Cap (Xtal2/Tosc2)
ATmega169P
System Osc.
16 pF
6 pF
Timer Osc.
16 pF
6 pF
Table 8-9.
Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
SUT1..0
Additional Delay from Reset (V
CC = 5.0V)
Recommended Usage
00
14 CK
Fast rising power or BOD enabled
01
14 CK + 4 ms
Slowly rising power
10
14 CK + 65 ms
Stable frequency at start-up
11
Reserved
Table 8-10.
Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
CKSEL3..0
Start-up Time from
Power-down and Power-save
Recommended Usage
1K CK
0111
32K CK
Stable frequency at start-up
Ce Ci
+
2
CL
Cs
–
=