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CHAPTER 8 16-BIT TIMER/EVENT COUNTER
User’s Manual U12697EJ3V0UM
(3) Pulse width measurement with free-running counter and two capture registers
When 16-bit timer counter 0 (TM0) is used as a free-running counter (refer to
Figure 8-16
), the pulse width of
the signal input to the TI00/P35 pin can be measured.
When the edge specified by bits 4 and 5 (ES00 and ES01) of prescaler mode register 0 (PRM0) is input to the
TI00/P35 pin, the value of TM0 is loaded to 16-bit capture/compare register 01 (CR01), and an external interrupt
request signal (INTTM01) is set.
The value of TM0 is also loaded to 16-bit capture/compare register 00 (CR00) when an edge reverse to the one
that triggers capturing to CR01 is input.
The edge of the TI00/P35 pin is specified by bits 4 and 5 (ES00 and ES01). The rising or falling edge can be
specified.
The valid edge of TI00/P35 pin is detected through sampling at a count clock cycle selected by prescaler mode
register 0 (PRM0), and the capture operation is not performed until the valid level is detected two times. Therefore,
noise with a short pulse width can be rejected.
Caution If the valid edge of the TI00/P35 pin is specified to be both the rising and falling edges,
capture/compare register 00 (CR00) cannot perform its capture operation.
Figure 8-16. 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/P35 pin.
CR01 as capture register
Remark
0/1:
When these bits are reset to 0 or set to 1, the other functions can be used along with the pulse
width measurement function. For details, refer to
Figures 8-2
and
8-3
.
