UPD784938 Datasheet, PDF (524/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 22 EDGE DETECTION FUNCTION
22.5 Cautions
(1) Valid edge detection cannot be performed when the valid edge is changed by a write to the external interrupt mode
register (INTMn: n = 0, 1). Also, if an edge is input during a change of the valid edge, that edge may or may not be
judged to be a valid edge.
(2) 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.
(3) Since digital noise elimination is performed on the P21 pin with the fSMP clock, there is a delay of 2 to 3 fSMP clocks
between input of an edge to the pin and the point at which the edge is actually detected.
(4) If the input pulse width on the P21 pin is 2 to 3 fSMP clocks, it is uncertain whether a valid edge will be detected. Therefore,
to ensure reliable operation, the level should be held for at least 3 clocks.
(5) If noise input of the P21 pin is synchronized with the fSMP clock in the µPD784938, it may not be recognized as noise.
If there is a possibility of such noise being input, noise should be eliminated by adding a filter to the input pins.
(6) Since digital noise elimination is performed on pins P22 to P24 with the fCLK clock, there is a delay of 2 to 3 fCLK clocks
between input of an edge to the pin and the point at which the edge is actually detected.
(7) If the input pulse width on pins P22 to P24 is 2 to 3 fCLK clocks, it is uncertain whether a valid edge will be detected.
Therefore, to ensure reliable operation, the level should be held for at least 3 clocks.
(8) If noise input to pins P22 to P24 is synchronized with the fCLK clock in the µPD784938, it may not be recognized as
noise. If there is a possibility of such noise being input, noise should be eliminated by adding a filter to the input pins.
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Preliminary User’s Manual U13987EJ1V0UM00