Hardware Reference
In-Depth Information
7
6
5
4
3
2
1
0
C7F
C6F
C5F
C4F
C3F
C2F
C1F
C0F
Reset:
0
0
0
0
0
0
0
0
C
F: input-capture/output-compare interrupt flag bits
0 = interrupt condition has not occurred.
1 = interrupt condition has occurred.
n
Figure 8.8
■
Timer Interrupt Flag register 1 (TFLG1)
To clear a flag in the TFLG1 register, write a 1 to it. However, there is a better way to clear the
flag that incurs less overhead. Setting bit 4 (TFFCA) of the TSCR1 register allows clearing a flag by
reading the corresponding input-capture register or writing a new value into the output-compare
register. This operation is needed for the normal operation of the input-capture or output-compare
function.
Each input-capture channel has a 16-bit register (TC
x
,
x
5 0 to 7) to hold the count value
when the selected signal edge arrives at the pin. This register is also used as the output-compare
register when the output-compare function is selected instead.
There are many applications for the input-capture function. Examples include the following:
•
Event arrival-time recording
. Some applications, for example, swimming
competitions, need to compare the arrival times of several different swimmers.
The input-capture function is very suitable for this application. The number of
events that can be compared is limited by the number of input-capture channels.
•
Period measurement
. To measure the period of an unknown signal, the input-
capture function should be configured to capture the timer values corresponding
to two consecutive rising or falling edges, as illustrated in Figure 8.9.
•
Pulse-width measurement
. To measure the width of a pulse, two adjacent rising
and falling edges are captured, as shown in Figure 8.10.
One period
(a) Capture two rising edges
One period
(b) Capture two falling edges
Figure 8.9
■
Period measurement by capturing two consecutive edges
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