CHAPTER 7 TIMER/COUNTER FUNCTION
161
7.2.3 Pulse width measurement
The 16-bit timer register n (TMn) can be used to measure the pulse widths of the signals input to the TIn0 and
TIn1 pins.
Measurement can be carried out with TMn used as a free running counter or by restarting the timer in
synchronization with the edge of the signal input to the TIn0 pin.
(1) Pulse width measurement with free running counter and one capture register
If the edge specified by the prescaler mode register n (PRMn) is input to the TIn0 pin when the 16-bit timer
register n (TMn) is used as a free running counter (refer to Figure 7-11), the value of TMn is loaded to the 16-bit
capture/compare register n1 (CRn1), and an external interrupt request signal (INTTMn1) is set.
The edge is specified by using bits 6 and 7 (ESn10 and ESn11) of the prescaler mode register n (PRMn). The
rising edge, falling edge, or both the rising and falling edges can be selected.
The valid edge is detected through sampling at a count clock cycle selected by the prescaler mode register n
(PRMn), 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.
Figure 7-11. Control Register Settings for Pulse Width Measurement with
Free Running Counter and One Capture Register
(a) 16-bit timer mode control register 0, 1 (TMC0, TMC1)
TMCn3
TMCn2
TMCn1
OVFn
TMCn
0
0
0
0
0
1
0/1
0
Free running mode
(b) Capture/compare control register 0, 1 (CRC0, CRC1)
CRCn2
CRCn1
CRCn0
CRCn
0
0
0
0
0
1
0/1
0
CRn0 as compare
register
CRn1 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 7-2 and 7-3.
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