NXP Semiconductors Kinetis KE1xZ256, Reference Manual

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Similarly, when the channel (n+1) CHF bit is set, both edges were captured and the
captured values are ready for reading in the C(n)V and C(n+1)V registers.
39.5.26.2 Continuous Capture mode
The Continuous Capture mode is selected when (DECAPEN = 1), and (channel (n) MSA
= 1). In this capture mode, the edges at the channel (n) input are captured continuously.
The channel (n) ELSB:ELSA bits select the initial edge to be captured, and channel (n+1)
ELSB:ELSA bits select the final edge to be captured.
The edge captures are enabled while DECAP bit is set. For the initial use, first the
channel (n) CHF and channel (n+1) CHF bits must be cleared, and then DECAP bit must
be set to start the continuous measurements.
When the channel (n+1) CHF bit is set, both edges were captured and the captured values
are ready for reading in the C(n)V and C(n+1)V registers. The latest captured values are
always available in these registers even after the DECAP bit is cleared.
In this mode, it is possible to clear only the channel (n+1) CHF bit. Therefore, when the
channel (n+1) CHF bit is set again, the latest captured values are available in C(n)V and
C(n+1)V registers.
For a new sequence of the measurements in the Dual Edge Capture – Continuous mode,
clear the channel (n) CHF and channel (n+1) CHF bits to start new measurements.
39.5.26.3 Pulse width measurement
If the channel (n) is configured to capture rising edges (channel (n) ELSB:ELSA = 0:1)
and the channel (n+1) to capture falling edges (channel (n+1) ELSB:ELSA = 1:0), then
the positive polarity pulse width is measured. If the channel (n) is configured to capture
falling edges (channel (n) ELSB:ELSA = 1:0) and the channel (n+1) to capture rising
edges (channel (n+1) ELSB:ELSA = 0:1), then the negative polarity pulse width is
measured.
The pulse width measurement can be made in One-Shot Capture mode or Continuous
Capture mode .
The following figure shows an example of the Dual Edge Capture – One-Shot mode used
to measure the positive polarity pulse width. The DECAPEN bit selects the Dual Edge
Capture mode, so it remains set. The DECAP bit is set to enable the measurement of next
positive polarity pulse width. The channel (n) CHF bit is set when the first edge of this
pulse is detected, that is, the edge selected by channel (n) ELSB:ELSA bits. The channel
(n+1) CHF bit is set and DECAP bit is cleared when the second edge of this pulse is
Chapter 39 FlexTimer Module (FTM)
Kinetis KE1xZ256 Sub-Family Reference Manual, Rev. 3, 07/2018
NXP Semiconductors 975