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IVI signal
IHI signal
divided
waveform
FRC
ICRB
Figure 13.9 Timing Chart for Measurement of IVI Signal and
13.4.4
2fH Modification of IHI Signal
By using the timer connection and FRT, even if there is a part of the IHI signal with twice the
frequency, this can be eliminated. In order for this function to operate properly, the duty cycle of
the IHI signal must be approximately 30% or less, or approximately 70% or above.
The 8-bit OCRDM contents or twice the OCRDM contents can be added automatically to the data
captured in ICRD of the FRT, and compare-matches generated at these points. The interval
between the two compare-matches is called a mask interval. A value equivalent to approximately
1/3 the IHI signal period is written to OCRDM. ICRD is set so that capture is performed on the
rise of the IHI signal. Figure 13.10 shows a block diagram for 2fH modification of the IHI signal.
Since the IHI signal supplied to the IHO signal selection circuit is normally set on the rise of the
IHI signal and reset on the fall, its waveform is the same as that of the original IHI signal. When
2fH modification is selected, IHI signal edge detection is disabled during mask intervals. Capture
is also disabled during these intervals.
Examples of TCR, TCSR, TOCR, and OCRDM settings of the FRT are shown in table 13.8, and
the 2fH modification timing chart is shown in figure 13.11.
ICRB(2)
ICRB(1)
IHI Signal Divided Waveform Periods
ICRB(4)
ICRB(3)
Rev. 1.00, 09/03, page 387 of 704
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