Datasheet

Compared to the 32.768 kHz crystal oscillator, this oscillator offers a faster startup time and is less exposed to the

external environment, as it is fully integrated. However

, its output frequency is subject to larger variations with supply

voltage, temperature and manufacturing process. Therefore, the user must take these variations into account when

this oscillator is used as a time base (startup counter, frequency monitor, etc.). Refer to the section “Electrical

Characteristics”.

This oscillator is disabled by clearing the SUPC_CR.XTALSEL.

Related Links

58. Electrical Characteristics for SAM V70/V71

59. Electrical Characteristics for SAM E70/S70

30.4.2 32.768 kHz Crystal Oscillator

By default, the 32.768 kHz oscillator is disabled. To use this oscillator, the XIN32 and XOUT32 pins must be

connected to a 32.768 kHz crystal or to a ceramic resonator. Refer to the section “Electrical Characteristics” for

appropriate loading capacitors selection on XIN32 and XOUT32.

Note that the user is not obliged to use the 32.768 kHz crystal oscillator and can use the Slow RC oscillator instead.

Using the 32.768 kHz crystal oscillator provides a more accurate frequency than the Slow RC oscillator.

To select the 32.768 kHz crystal oscillator as the source of SLCK, the bit SUPC_CR.XTALSEL must be set. This

results in a sequence which first configures the PIO lines multiplexed with XIN32 and XOUT32 to be driven by the

crystal oscillator, then enables the 32.768 kHz crystal oscillator and then disables the Slow RC oscillator to save

power. The switch of SLCK source is glitch-free.

Reverting to the Slow RC oscillator is only possible by shutting down the VDDIO power supply. If the user does not

need the 32.768 kHz crystal oscillator, the XIN32 and XOUT32 pins can be left unconnected since by default the

XIN32 and XOUT32 system I/O pins are in PIO input mode with pullup after reset.

The user can also set the 32.768 kHz crystal oscillator in Bypass mode instead of connecting a crystal. In this case,

the user must provide the external clock signal on XIN32. For input characteristics of the XIN32 pin, refer to the

section “Electrical Characteristics”. To enter Bypass mode, the OSCBYPASS bit of the Supply Controller Mode