41.5.2.1 Initialization

The FREQM bus clock (CLK_FREQM_APB) is required to access the FREQM registers. This clock can be enabled in the MCLK - Main Clock module.

Before enabling FREQM, the device and peripheral must be configured:
  • Each of the generic clocks (GCLK_FREQM_REF and GCLK_FREQM_MSR) must be configured and enabled.
    Important: The reference clock must be slower than the measurement clock.
  • Write the number of Reference clock cycles for which the measurement is to be done in the Configuration A register (CFGA.REFNUM). This must be a non-zero number.

The following register is enable-protected, that is, it can only be written when the FREQM is disabled: (CTRLA.ENABLE = 0):The Configuration A register (CFGA)

Enable-protection is denoted by the "Enable-Protected" property in the register description.