Data Sheet

Silicon Labs
Page 22 of 45
6.10 32.768 kHz External Reference Clock
Pad number Function Description
33 SOSCI External 32.768 kHz crystal input
34 SOSCO External 32.768 kHz crystal output
Table 11: Slow clock crystal pads
The module contains integrated RC oscillators for sleep timing, one in the WiFi chipset, one in the CPU. The
sleep clocks are used to periodically wake up the module while in power save modes. If more accurate timing
is required, an external 32.768 kHz crystal and the associated capacitors can be placed to pads SOSCI and
SOSCO. If an accurate sleep clock is not needed, the pads are available for GPIO use.
An external oscillator can also be used to generate the sleep clock. The voltage levels should be 3.3V logic
level.
This low frequency clock is shared for both the CPU and the WiFi chipset. The default WiFi configuration uses
only the internal oscillator, if support for a crystal stabilized WiFi sleep clock is required, please contact
Bluegiga technical support.
The Wi-Fi packet timing during active data transfer is derived from the internal 26MHz crystal and so is
unaffected by the tolerances of the sleep clock.
Notice: If the module internal RTC (Real Time Clock) is in use, the External Reference Clock is mandatory.
Initializing the RTC without a 32kHz crystal connected will cause the module to freeze while waiting for the
oscillator to start up.