Datasheet

• Control B register (CTRLB)
• Interrupt Flag Status and Clear register (INTFLAG)
• Status register (STATUS)
Optional write protection by the Peripheral Access Controller (PAC) is denoted by the "PAC Write
Protection" property in each individual register description.
Write-protection does not apply to accesses through an external debugger.
Related Links
27. PAC - Peripheral Access Controller
30.6 Functional Description
30.6.1 Principle of Operation
FREQM counts the number of periods of the measured clock (GCLK_FREQM_MSR) with respect to the
reference clock (GCLK_FREQM_REF). The measurement is done for a period of REFNUM/f
CLK_REF
and
stored in the Value register (VALUE.VALUE). REFNUM is the number of Reference clock cycles selected
in the Configuration A register (CFGA.REFNUM).
The frequency of the measured clock,

CLK_MSR
, is calculated by

CLK_MSR
=
VALUE
REFNUM

CLK_REF
30.6.2 Basic Operation
30.6.2.1 Initialization
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, meaning that it can only be written when the FREQM is
disabled (CTRLA.ENABLE=0):
• Configuration A register (CFGA)
Enable-protection is denoted by the "Enable-Protected" property in the register description.
Related Links
14. GCLK - Generic Clock Controller
30.6.2.2 Enabling, Disabling and Resetting
The FREQM is enabled by writing a '1' to the Enable bit in the Control A register (CTRLA.ENABLE). The
peripheral is disabled by writing CTRLA.ENABLE=0.
SAM D5x/E5x Family Data Sheet
FREQM – Frequency Meter
© 2019 Microchip Technology Inc.
Datasheet
DS60001507E-page 833