98
8331B–AVR–03/12
Atmel AVR XMEGA AU
Note:
Refer to Electrical characteristics section in device datasheet to retrieve the best setting for a
given frequency.
• Bit 5 – X32KLPM: Crystal Oscillator 32.768kHz Low Power Mode
Setting this bit enables the low power mode for the 32.768kHz crystal oscillator. This will reduce
the swing on the TOSC2 pin.
• Bit 4 – XOSCPWR: Crystal Oscillator Drive
Setting this bit will increase the current in the 0.4MHz - 16MHz crystal oscillator and increase the
swing on the XTAL2 pin. This allows for driving crystals with higher load or higher frequency
than specfiied by the FRQRANGE bits.
• Bit 3:0 – XOSCSEL[3:0]: Crystal Oscillator Selection
These bits select the type and start-up time for the crystal or resonator that is connected to the
XTAL or TOSC pins. See
for crystal selections. If an external clock or external oscilla-
tor is selected as the source for the system clock, see
”CTRL – Oscillator Control register” on
. This configuration cannot be changed.
Notes:
1. This option should be used only when frequency stability at startup is not important for the
application. The option is not suitable for crystals.
2. This option is intended for use with ceramic resonators. It can also be used when the fre-
quency stability at startup is not important for the application.
3. When the external oscillator is used as the reference for a DFLL, only EXTCLK and 32KHZ
can be selected.
Table 7-7.
16MHz crystal oscillator frequency range selection.
FRQRANGE[1:0]
Group Configuration
Typical Frequency
Range
Recommended Range for
Capacitors C1 and C2 (pF)
00
04TO2
0.4MHz - 2MHz
100-300
01
2TO9
2MHz - 9MHz
10-40
10
9TO12
9MHz - 12MHz
10-40
11
12TO16
12MHz - 16MHz
10-30
Table 7-8.
External oscillator selection and start-up time.
XOSCSEL[3:0]
Group Configuration
Selected Clock Source
Start-up Time
0000
EXTCLK
External Clock
6 CLK
0010
32KHZ
32.768kHz TOSC
16K CLK
0011
XTAL_256CLK
0.4MHz - 16MHz XTAL
256 CLK
0111
XTAL_1KCLK
0.4MHz - 16MHz XTAL
1K CLK
1011
XTAL_16KCLK
0.4MHz - 16MHz XTAL
16K CLK
