Datasheet

SAM9G45 [DATASHEET]
Atmel-6438O-ATARM-SAM9G45-Datasheet_08-Dec-15
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24.3 Slow Clock Crystal Oscillator
The Clock Generator integrates a 32,768 Hz low-power oscillator. The XIN32 and XOUT32 pins must be
connected to a 32,768 Hz crystal. Two external capacitors must be wired as shown in Figure 24-2.
Figure 24-2. Typical Slow Clock Crystal Oscillator Connection
24.4 Slow Clock RC Oscillator
The user has to take into account the possible drifts of the RC Oscillator. More details are given in Section 45.2
“DC Characteristics”.
24.5 Slow Clock Selection
The slow clock can be generated either by an external 32,768 Hz crystal or by the on-chip RC oscillator. The
32768 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 32768 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.
Figure 24-3. Slow Clock Selection
RCEN, OSC32EN,OSCSEL and OSC32BYP bits are located in the Slow Clock Configuration 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