Information

35.4.24.2 Continuous Capture mode
The Continuous Capture mode is selected when (FTMEN = 1), (DECAPEN = 1), and
(MS(n)A = 1). In this capture mode, the edges at the channel (n) input are captured
continuously. The ELS(n)B:ELS(n)A bits select the initial edge to be captured, and
ELS(n+1)B:ELS(n+1)A bits select the final edge to be captured.
The edge captures are enabled while DECAP bit is set. For the initial use, first the
CH(n)F and CH(n+1)F bits must be cleared, and then DECAP bit must be set to start the
continuous measurements.
When the CH(n+1)F 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 CH(n+1)F bit. Therefore, when the CH(n+1)F
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 CH(n)F and CH(n+1)F bits to start new measurements.
35.4.24.3 Pulse width measurement
If the channel (n) is configured to capture rising edges (ELS(n)B:ELS(n)A = 0:1) and the
channel (n+1) to capture falling edges (ELS(n+1)B:ELS(n+1)A = 1:0), then the positive
polarity pulse width is measured. If the channel (n) is configured to capture falling edges
(ELS(n)B:ELS(n)A = 1:0) and the channel (n+1) to capture rising edges (ELS(n
+1)B:ELS(n+1)A = 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 CH(n)F bit is set when the first edge of this pulse is
detected, that is, the edge selected by ELS(n)B:ELS(n)A bits. The CH(n+1)F bit is set
and DECAP bit is cleared when the second edge of this pulse is detected, that is, the edge
selected by ELS(n+1)B:ELS(n+1)A bits. Both DECAP and CH(n+1)F bits indicate when
two edges of the pulse were captured and the C(n)V and C(n+1)V registers are ready for
reading.
Functional description
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
802 Freescale Semiconductor, Inc.