Information

The following figure shows an example of the Dual Edge Capture – One-Shot mode used
to measure the period between two consecutive rising edges. The DECAPEN bit selects
the Dual Edge Capture mode, so it remains set. The DECAP bit is set to enable the
measurement of next period. The CH(n)F bit is set when the first rising edge 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 rising edge 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 selected
edges were captured and the C(n)V and C(n+1)V registers are ready for reading.
channel (n) input
(after the filter
DECAPEN bit
C(n+1)V
FTM counter
clear CH(n+1)F
problem 2
2
1
2
3
channel input)
DECAP bit
set DECAPEN
set DECAP
5
6
7
8
10
3
4
6
5
Note
- The commands set DECAPEN, set DECAP, clear CH(n)F, and clear CH(n+1)F are made by the user.
4
9
11
12
13
14
6
15
16
17
18
19
20
21
22
23
24
25
26
27
28
17
20
15
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23
C(n)V
CH(n+1)F bit
CH(n)F bit
clear CH(n)F
1
- Problem 1: channel (n) input = 0, set DECAP, not clear CH(n)F, and not clear CH(n+1)F.
- Problem 2: channel (n) input = 1, set DECAP, not clear CH(n)F, and clear CH(n+1)F.
- Problem 3: channel (n) input = 1, set DECAP, not clear CH(n)F, and not clear CH(n+1)F.
problem 3
problem 1
7
9
18 26
18
14
27
7
Figure 35-206. Dual Edge Capture – One-Shot mode to measure of the period between
two consecutive rising edges
The following figure shows an example of the Dual Edge Capture – Continuous mode
used to measure the period between two consecutive rising edges. The DECAPEN bit
selects the Dual Edge Capture mode, so it remains set. While the DECAP bit is set the
configured measurements are made. The CH(n)F bit is set when the first rising edge is
detected, that is, the edge selected by ELS(n)B:ELS(n)A bits. The CH(n+1)F bit is set
Chapter 35 FlexTimer Module (FTM)
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
Freescale Semiconductor, Inc. 803