Fujitsu F2MC-16LX Hardware Manual page 398

CHAPTER 15 PWC TIMER
Minimum pulse width
There are following limitations for pulses that can be input to width measurement input terminals:
• Minimum pulse width: 2 divisions of machine clock (0.25µs or more for 16-MHz machine clock)
• Minimum input frequency: 4 divisions of machine clock (4 MHz or less for 16-MHz machine clock)
When the input pulse width is smaller or the input pulse frequency is higher than the above description, the
operation cannot be guaranteed. If there is a possibility of such noise in the input signal, use, for example, a
filter outside of the chip to eliminate the noise before the signal is input.
Frequency of dividing frequency measurement mode
Note that the pulse width obtained from the measured result calculation is the average value because the
input pulses are divided in the division cycle measurement mode among the pulse width measurement
modes.
Handling of clock select bit
Do not set "11
Reactivation under operation
When restarting after starting the count operation, following cases may occur depending on the timing:
• When restarting at the same time of an overflow occurrence in the reload timer mode, the overflow flag
(OVIR) is set.
• When restarting at the same time of measurement termination edge input in the pulse width single
measurement mode, the measurement start edge is waited and the measurement termination edge
(EDIR) is set.
• When restarting at the same time of measurement termination edge input in the pulse width single
measurement mode, the measurement start edge is waited and the measurement termination edge
(EDIR) is set and the current measured result is transferred to the PWCR.
When the PWC timer is used in "the "H" pulse-width or "L" pulse-width measurement mode in the
continuous measurement mode":
The pulse width measurement is completed, the next pulse width measurement start is waited, the timer
operation is unexpectedly continued, and the overflow flag (OVIR) of timer may be sometime set before
starting the next pulse width measurement. In this case, even when no overflow occurs at the next pulse
width measurement termination, the overflow flag has been set. Therefore, do not use the overflow flag
when using the PWC timer in the "H" pulse width or "L" pulse width measurement mode in the continuous
measurement mode.
382
" to (Bit 7, 6) CKS1, CKS0 (clock selection) in the PWCSR.
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