HD404374 Datasheet, PDF (53/161 Pages) Renesas Technology Corp – Low-Voltage AS Microcomputers with On-Chip A/D Converter

HD404374/HD404384/HD404389/HD404082/HD404084 Series
Usage notes (Applies to HD404374 Series):
In watch mode and subactive mode, an interrupt will not be detected correctly if the INT₀ or WU₀ high or
low-level period is shorter than the interrupt frame period.
The MCU’s edge sensing method is shown in figure 18. The MCU samples the INT₀ and WU₀ signals at
regular intervals, and if consecutive sampled values change from high to low, it determines that a falling
edge has been generated.
Interrupt detection errors occur since this sampling is performed at the interrupt frame period. If the high-
level period of the INT₀ or WU₀ signal is within an interrupt frame, as shown in figure 19 (a), the signal will
be low at point A and point B, with the result that the falling edge will not be recognized. Similarly, If the
low-level period of the INT₀ or WU₀ signal is within an interrupt frame, as shown in figure 19 (b), the
signal will be high at point A and point B, with the result that the falling edge will not be recognized.
In watch mode and subactive mode, therefore, ensure that the high-level and low-level periods of the INT₀
and
WU
0
signals
is
at
least
as
long
as
the
interrupt
frame
period.
0
or
0
Sampling
High
Low
Low
Figure 18 Edge Sensing Method
(a) High-level mode
0 or 0
(b) Low-level mode
0 or 0
Interrupt frame Point A: Low
Point B: Low Interrupt frame Point A: High
Point B: High
Figure 19 Sampling Examples
Rev.5.00, Sep.11.2003, page 53 of 161