Atmel Evaluation Kit AT91SAM9M10-G45-EK AT91SAM9M10-G45-EK データシート

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SAM9M10 [DATASHEET]

6355F–ATARM–12-Mar-13

The Clock Generator integrates a 32,768 Hz low-power oscillator. The XIN32 and XOUT32 pins must be con-
nected to a 32,768 Hz crystal. Two external capacitors must be wired as shown in 

Figure 25-2

.

Typical Slow Clock Crystal Oscillator Connection

The user has to take into account the possible drifts of the RC Oscillator. More details are given in the section “DC
Characteristics” of the product datasheet.

The SAM9M10 slow clock can be generated either by an external 32,768 Hz crystal or by the on-chip RC oscillator.
The 32,768 Hz crystal oscillator can be bypassed by setting the bit OSC32BYP to accept an external slow clock on
XIN32. 

The internal RC oscillator and the 32,768 Hz oscillator can be enabled by setting to 1, respectively, RCEN bit and
OSC32EN bit in the System Controller user interface. The OSCSEL command selects the slow clock source.

Slow Clock Selection

RCEN, OSC32EN,OSCSEL and OSC32BYP bits are located in the Slow Clock Control Register (SCKCR) located
at address 0xFFFFFD50 in the backed up part of the System Controller and so are preserved while VDDBU is
present.

After a VDDBU power on reset, the default configuration is RCEN=1, OSC32EN=0 and OSCSEL=0, allowing the
system to start on the internal RC oscillator.

The programmer controls the slow clock switching by software and so must take precautions during the switching
phase.

XIN32

XOUT32

GNDOSC

32,768 Hz 

Crystal

On Chip 
RC OSC

Slow Clock 
SLCK

XIN32

XOUT32

Slow Clock

Oscillator

Clock Generator

OSC32EN

RCEN

OSCSEL

OSC32BYP