UPD784938 Datasheet, PDF (521/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 22 EDGE DETECTION FUNCTION
22.2 Edge Detection for Pins P20, P25, and P26
On pins P20, P25, and P26, noise elimination is performed by means of analog delay before edge detection. Therefore,
an edge cannot be detected unless the pulse width is a given time (10 µs) or longer.
Figure 22-4. Edge Detection for Pins P20, P25, and P26
P20/P25/P26 input
P20/P25/P26 input signal
after noise elimination
10 µs (MIN.)
10 µs
(MAX.)
10 µs
(MAX.)
Rising edge
Falling edge
Eliminated as noise
since pulse is short
Eliminated as noise
since pulse is short _{Falling edge detected since}
Rising edge detected since
pulse is sufficiently wide
pulse is suficiently wide
Caution Since analog delay noise elimination is performed on pins P20, P25, and P26, an edge is detected up
to 10 µs after it is actually input. Also, unlike pins P21 to P24, the delay before an edge is detected
is not a specific value, because of differences in the characteristics of various devices.
Preliminary User’s Manual U13987EJ1V0UM00
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