HD404374FT datasheet(53/161 Pages) RENESAS

53 / 161 page

HD404374/HD404384/HD404389/HD404082/HD404084 Series

Rev.5.00, Sep.11.2003, page 53 of 161

Usage notes (Applies to HD404374 Series):

In watch mode and subactive mode, an interrupt will not be detected correctly if the

INT

0 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 INT

0 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 INT

0 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 INT

0 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

INT

and

0 signals is at least as long as the interrupt frame period.

Sampling

High

Low

Figure 18 Edge Sensing Method

Interrupt frame

Point A: Low

Point B: Low

Interrupt frame

Point A: High

Point B: High

(a) High-level mode

(b) Low-level mode

Figure 19 Sampling Examples

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