
93
XMEGA A [MANUAL]
8077I–AVR–11/2012
Bit 7:6 – PLLSRC[1:0]: Clock Source
The PLLSRC bits select the input source for the PLL according to
Table 7-7.Table 7-7.
PLL clock source.
Notes:
1.
The 32.768kHz TOSC cannot be selected as the source for the PLL. An external clock must be a minimum 0.4MHz to be used as the source clock.
Bit 5 – Reserved
This bit is unused and reserved for future use. For compatibility with future devices, always write this bit to zero when this
register is written.
Bit 4:0 – PLLFAC[4:0]: Multiplication Factor
These bits select the multiplication factor for the PLL. The multiplication factor can be in the range of from 1x to 31x.
7.10.7 DFLLCTRL – DFLL Control register
Bit 7:3 – Reserved
These bits are unused and reserved for future use. For compatibility with future devices, always write these bits to zero
when this register is written.
Bit 2:1 – RC32MCREF[1:0]: 32MHz Oscillator Calibration Reference
These bits are used to select the calibration source for the 32MHz DFLL according to the
Table 7-8. These bits will select
only which calibration source to use for the DFLL. In addition, the actual clock source that is selected must enabled and
configured for the calibration to function.
Table 7-8.
32MHz oscillator reference selection.
Bit 0 – RC2MCREF: 2MHz Oscillator Calibration Reference
This bit is used to select the calibration source for the 2MHz DFLL. By default, this bit is zero and the 32.768kHz internal
oscillator is selected. If this bit is set to one, the 32.768kHz crystal oscillator on TOSC is selected as the reference. This
PLLSRC[1:0]
Group Configuration
PLL Input Source
00
RC2M
2MHz internal oscillator
01
—
Reserved
10
RC32M
32MHz internal oscillator
11
XOSC
Bit
76543
2
1
0
+0x06
–
RC32MCREF[1:0]
RC2MCREF
Read/Write
RRRRR
R/W
Initial Value
00000
0
RC32MCREF[1:0]
Group Configuration
Description
00
RC32K
32.768kHz internal oscillator
01
XOSC32
32.768kHz crystal oscillator on TOSC
10
—
Reserved
11
—
Reserved