CHAPTER 9 TIMER/COUNTER FUNCTION (REAL-TIME PULSE UNIT)
User’s Manual U12688EJ4V0UM00
279
(4) Operation for frequency measurement (Timer 1)
Timer 1 can measure the frequency of an external pulse’s input to pins INTP1n0 to INTP1n3 (n = 0 to 5).
Here, an example is shown where timer 1 and the capture/compare register CC110 are combined to measure
the frequency of an external pulse input to the INTP110 pin with 16-bit precision.
The active edge of the INTP110 input signal is specified to be the rising edge by the INTM2 register.
The frequency is calculated by determining the difference between the TM11 count value (Dn) captured in
the CC110 register from the nth rising edge, and the count value (Dn–1) captured from the rising edge the
(n – 1)th time, then multiplying this value by the count clock.
Figure 9-19. Example of Frequency Measurement Timing
FFFFH
FFFFH
FFFFH
D0
D1
D2
t1
t2
D0
D1
D2
TM11 count value
0
Interrupt request
(INTP110)
Capture/compare register
(CC110)
t1 = {(10000H – D0) + D1}
×
count clock cycle frequency
t2 = {(10000H – D0) + D2}
×
count clock cycle frequency
Remark
D0 to D2: TM11 count value
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