Datasheet

XMEGA B [DATASHEET]

8291B–AVR–01/2013

 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 7-10. 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 7-10. 32MHz oscillator reference design.

 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

bit 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.

7.11 Register Description – DFLL32M/DFLL2M

7.11.1 CTRL – Control register

 Bit 7:1 – 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 0 – ENABLE: Enable

Setting this bit enables the DFLL and auto-calibration of the internal oscillator. The reference clock must be enabled and

stable before the DFLL is enabled.

After disabling the DFLL, the reference clock can not be disabled before the ENABLE bit is read as zero.

7.11.2 CALA – Calibration register A

The CALA and CALB registers hold the 13-bit DFLL calibration value that is used for automatic run-time calibration of the

internal oscillator. When the DFLL is disabled, the calibration registers can be written by software for manual run-time

calibration of the oscillator. The oscillators will also be calibrated according to the calibration value in these registers

when the DFLL is disabled.

RC32MCREF[1:0] Group Configuration Description

00 RC32K 32.768kHz internal oscillator

01 XOSC32 32.768kHz crystal oscillator on TOSC

10 USBSOF USB start of frame

11 — Reserved

Bit 7 6 5 4 3 2 1 0

+0x00

– – – – – – – ENABLE

Read/Write R R R R R R R R/W

Initial Value 0 0 0 0 0 0 0 0

Bit 7 6 5 4 3 2 1 0

+0x02

– CALA[6:0]

Read/Write R R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 x x x x x x x