95
8331B–AVR–03/12
Atmel AVR XMEGA AU
• Bit 0 – RTCEN: RTC Clock Source Enable
Setting the RTCEN bit enables the selected RTC clock source for the real-time counter.
7.9.5
USBSCTRL – USB Control register
• Bit 7:6 – 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 5:3 – USBPSDIV[2:0]: USB Prescaler Division Factor
These bits define the division ratio of the USB clock prescaler according to
. These bits are locked as long as the USB clock source is enabled.
• Bit 2:1 – USBSRC[1:0]: USB Clock Source
These bits select the clock source for the USB module according to
Note:
1. The 32MHz internal oscillator must be calibrated to 48MHz before selecting this as source for
the USB device module. Refer to
”DFLL 2MHz and DFLL 32MHz” on page 89
• Bit 0 – USBSEN: USB Clock Source Enable
Setting this bit enables the selected clock source for the USB device module.
Bit
7
6
5
4
3
2
1
0
–
–
USBPSDIV[2:0]
USBSRC[1:0]
USBSEN
USBSCTRL
Read/Write
R
R
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Table 7-5.
USB prescaler division factor.
USBPSDIV[2:0]
Group Configuration
Description
000
1
No division
001
2
Divide by 2
010
4
Divide by 4
011
8
Divide by 8
100
16
Divide by 16
101
32
Divide by 32
110
—
Reserved
111
—
Reserved
Table 7-6.
USB clock source.
USBSRC[1:0]
Group Configuration
Description
00
PLL
PLL
01
RC32M
32MHz internal oscillator
