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CHAPTER 6 16-BIT TIMER/EVENT COUNTER 0
User
’
s Manual U14701EJ3V0UD
(3) Pulse width measurement with free-running counter and two capture registers
When 16-bit timer counter 0 (TM0) is operated in free-running mode (see register settings in
Figure 6-17
), it is
possible to measure the pulse width of the signal input to the TI00/P31 pin.
When the edge specified by bits 4 and 5 (ES00 and ES01) of prescaler mode register 0 (PRM0) is input to the
TI00/P31 pin, the value of TM0 is taken into 16-bit timer capture/compare register 01 (CR01) and an interrupt
request signal (INTTM01) is set.
Also, on the inverse edge input of that of the capture operation into CR01, the value of TM0 is taken into 16-
bit timer capture/compare register 00 (CR00).
Either of two edges can be selected
—
rising or falling
—
as the valid edges for the TI00/P31 pin specified by means
of bits 4 and 5 (ES00 and ES01) of prescaler mode register 0 (PRM0).
Sampling is performed at the interval selected by means of prescaler mode register 0 (PRM0), and a capture
operation is only performed when a valid level of the TI00/P31 pin is detected twice, thus eliminating noise with
a short pulse width.
Caution If the valid edge of TI00/P31 pin is specified to be both rising and falling edges, 16-bit timer
capture/compare register 00 (CR00) cannot perform the capture operation.
Figure 6-17. Control Register Settings for Pulse Width Measurement with Free-Running Counter and
Two Capture Registers
(a) 16-bit timer mode control register 0 (TMC0)
0
0
0
0
TMC03
0
TMC02
1
TMC01
0/1
OVF0
0
TMC0
Free running mode
(b) Capture/compare control register 0 (CRC0)
0
0
0
0
0
CRC02
1
CRC01
1
CRC00
1
CRC0
CR00 as capture register
Captures to CR00 at edge reverse
to valid edge of TI00/P31.
CR01 as capture register
Remark
0/1: Setting 0 or 1 allows another function to be used simultaneously with pulse width measurement.
See the description of the respective control registers for details.