Fujitsu F2MC-16LX Hardware Manual page 318

CHAPTER 14 PWC TIMER
❍ Minimum pulse width
The following restrictions apply to pulses that can be input to the pulse width measurement input
pin.
Minimum pulse width: machine clock divided-by-2 (0.25 µs or more for 16 MHz machine
•
clock)
• Minimum input frequency: machine clock divided-by-4 (4 MHz or less for 16 MHz machine
clock)
If a pulse with lower width or higher frequency than specified above is input, correct operation
cannot be assured. In the event that the input signal might contain noise, eliminate the noise
using a filter externally from the chip before inputting the pulse.
❍ Divide frequency measurement mode
In divide interval measurement mode, which is one of the pulse width measurement modes, the
input pulse is divided. Note that the pulse width as calculated from the measurement results will
therefore be an averaged value.
❍ Handling of clock selection bit
Do not set [bits 7and 6] of the PWCR (clock selection bits CKS1 and CKS0) to 11
❍ Handling of reserved bit
[bit 8] in the PWCR is reserved. If necessary, clear this bit by writing 0.
❍ Restart during operation
Restarting after the count operation has been started may cause the following events depending
on the timing of restart:
• If, in reload timer mode, a restart occurs at the same time as an overflow:
The restart is performed, but the overflow flag (OVIR) is set.
• If, in pulse width one-shot measurement mode, a restart occurs at the same time as
detection of a measurement end edge:
Restart is performed when the measurement start edge wait state is entered, and the
measurement end edge flag (EDIR) is set.
• If, in pulse width repeated measurement mode, a restart occurs at the same time as
measurement end edge detection:
Restart is performed when the measurement start edge wait state is entered, but the
measurement end edge flag (EDIR) is set and the measurement result is transferred to the
PWCR.
❍ If the PWC timer is used in "H"-pulse or L- pulse width measurement mode of the repeated
measurement mode
If, after the end of pulse width measurement, the pulse width measurement start wait state is
entered, the timer to be stopped might continue with the overflow flag (OVIR) being set before
the pulse width measurement starts. In other words, even if no overflow occurs during the next
pulse width measurement phase, the overflow flag may be set. Therefore, do not use the
overflow flag when you use the PWC timer in "H"-pulse or "L"-pulse width measurement mode
of repeated measurement mode.
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