Before enabling FREQM, the device and peripheral must be configured:
- Each of the generic clocks (GCLK_FREQM_REF and GCLK_FREQM_MSR) should be configured
and enabled. Note that the reference clock should be slower than the measurement
clock.
- The Number of Reference Clock Cycles
value in the Configuration A register (CFGA.REFNUM) must be written to a value greater than
0x00.
The following register is enable-protected,
meaning that it can only be written when the FREQM is disabled (CTRLA.ENABLE is zero):
- Configuration A register (CFGA)
Enable-protection is denoted by the
"Enable-Protected" property in the register description.