Datasheet

238
32133D–11/2011
UC3D
17. Frequency Meter (FREQM)
Rev: 3.1.0.1
17.1 Features
• Accurately measures a clock frequency
• Selectable reference clock
• A selectable clock can be measured
• Ratio can be measured with 24-bit accuracy
17.2 Overview
The Frequency Meter (FREQM) can be used to accurately measure the frequency of a clock by
comparing it to a known reference clock.
17.3 Block Diagram
Figure 17-1. Frequency Meter Block Diagram
17.4 Product Dependencies
In order to use this module, other parts of the system must be configured correctly, as described
below.
17.4.1 Power Management
The device can enter a sleep mode while a measurement is ongoing. However, make sure that
neither CLK_MSR nor CLK_REF is stopped in the actual sleep mode. FREQM interrupts can
wake up the device from sleep modes when the measurement is done, but only from sleep
modes where CLK_FREQM is running. Please refer to the Power Manager chapter for details.
Counter
CLK_REF
CLK_MSR
REFSEL
REFNUM,
START
CLKSEL
START
VALUE
Timer
Trigger ISR