HD404889_03 Datasheet, PDF (62/197 Pages) Renesas Technology Corp – Low-Voltage AS Microcomputers with On-Chip LCD Circuit

HD404889/HD404899/HD404878/HD404868 Series
Usage notes:
In watch mode and subactive mode, an interrupt will not be detected correctly if the INT₀ or WU₀ to WU₃
high or low-level period is shorter than the interrupt frame period.
The MCU’s edge sensing method is shown in figure 20. The MCU samples the INT₀ and WU₀ to WU₃
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 to WU₃ signal is within an interrupt frame, as shown in figure 21 (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 to WU₃ signal is within an interrupt frame, as shown
in figure 21 (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
INT
0
and
WU
0
to
WU
3
signals
is
at
least
as
long
as
the
interrupt
frame
period.
INT0
or
WU0 to WU3
Sampling
High
Low
Low
(a) High-level mode
Figure 20 Edge Sensing Method
(b) Low-level mode
INT0 or
WU0 to WU3
Interrupt frame _{Point A: Low}
INT0 or
WU0 to WU3
Point B: Low
Interrupt frame _{Point A: High}
Point B: High
Figure 21 Sampling Examples
Rev.6.00, Sep.08.2003, page 62 of 197