# Internal Low-Speed Oscillator (ILO)¶

group group_sysclk_ilo

The ILO operates with no external components and outputs a stable clock at 32.768 kHz nominal.

The ILO is relatively low power and low accuracy. It is available in all power modes and can be used as a source for the Backup domain clock.

To ensure the ILO remains active in Hibernate mode, and across power-on-reset (POR) or brown out detect (BOD), firmware must call Cy_SysClk_IloHibernateOn().

Additionally, the ILO clock can be trimmed to +/- 1.5% of nominal frequency using a higher precision clock source. Use the Clock Measurement API to measure the current ILO frequency before trimming.

note

The ILO is always the source clock for the WDT (Watchdog Timer). Therefore:

• The WDT must be unlocked when making an ILO function call in the PDL

• It is recommended to always have the ILO enabled