Datasheet

32
ATmega169A/PA/329A/PA/649A/P/3290A/PA/6490A/P [DATASHEET]
8284E–AVR–02/2013
The Oscillator can operate in three different modes, each optimized for a specific frequency range. The operating
mode is selected by the fuses CKSEL3...1 as shown in Table 9-5.
Note: 1. This option should not be used with XTALs, only with ceramic resonators.
The CKSEL0 Fuse together with the SUT1...0 Fuses select the start-up times as shown in Table 9-6.
Notes: 1. These options should only be used when not operating close to the maximum frequency of the device, and only if
frequency stability at start-up is not important for the application. These options are not suitable for XTALs.
2. These options are intended for use with ceramic resonators and will ensure frequency stability at start-up. They can
also be used with XTALs when not operating close to the maximum frequency of the device, and if frequency stabil-
ity at start-up is not important for the application.
9.6 Low-frequency XTAL oscillator
The Low-frequency XTAL Oscillator is optimized for use with a 32.768kHz watch XTAL. When selecting XTALs,
load capacitance and XTAL’s Equivalent Series Resistance, ESR must be taken into consideration. Both values
are specified by the XTAL vendor.
ATmega329A/329PA oscillator is optimized for very low power consumption, and thus when selecting XTALs, see
Table 9-7 for maximum ESR recommendations on 9pF and 6.5pF XTALs
Table 9-5. XTAL oscillator operating modes.
CKSEL3..1
Frequency range
[MHz]
Recommended range for capacitors C1 and C2
for use with XTALs [pF]
100
(1)
0.4 - 0.9 –
101 0.9 - 3.0 12 - 22
110 3.0 - 8.0 12 - 22
111 8.0 - 12 - 22
Table 9-6. Start-up times for the XTAL 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 258CK
(1)
14CK + 4.1ms
Ceramic resonator, fast
rising power
0 01 258CK
(1)
14CK + 65ms
Ceramic resonator,
slowly rising power
010 1K CK
(2)
14CK
Ceramic resonator,
BOD enabled
011 1K CK
(2)
14CK + 4.1ms Ceramic resonator, fast
rising power
100 1K CK
(2)
14CK + 65ms Ceramic resonator,
slowly rising power
1
01 16K CK 14CK XTAL Oscillator, BOD
enabled
1
10 16K CK 14CK + 4.1ms XTAL Oscillator, fast
rising power
1
11 16K CK 14CK + 65ms XTAL Oscillator, slowly
rising power