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173
CHAPTER 8 16-BIT TIMER/COUNTER
(2) Measurement of two pulse widths with free running counter
The pulse widths of the two signals respectively input to the TI00 and TI01 pins can be measured when the 16-
bit timer register (TM0) is used as a free running counter (refer to
Figure 8-13
).
When the edge specified by bits 4 and 5 (ES00 and ES01) of the prescaler mode register 0 (PRM0) is input to
the TI00 pin, the value of the TM0 is loaded to the 16-bit capture/compare register 01 (CR01) and an external
interrupt request signal (INTTM00) is set.
When the edge specified by bits 6 and 7 (ES10 and ES11) of the prescaler mode register 0 (PRM0) is input to
the TI01 pin, the value of TM0 is loaded to the 16-bit capture/compare register 00 (CR00), and an external interrupt
request signal (INTTM01) is set.
The edges of the TI00 and TI01 pins are specified by bits 4 and 5 (ES00 and ES01) and bits 6 and 7 (ES10 and
ES11) of PRM0, respectively. The rising, falling, or both rising and falling edges can be specified.
The valid edge of TI00/P35 pin and TI01/P36 pin is detected through sampling at a count clock cycle selected
by the 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.
Fig
u
re 8-13. Control Register Settings for Measurement of Two Pulse Widths with Free Running Counter
(a) 16-bit timer mode control register (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)
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
.
0
0
0
0
0
CRC02
1
CRC01
0
CRC00
1
CRC0
CR00 as capture register
Captures valid edge of TI01/P36 pin to CR00.
CR01 as capture register