UPD78F1502AGK-GAK-AX Datasheet, PDF (396/1031 Pages) Renesas Technology Corp – 16-Bit Single-Chip Microcontrollers

78K0R/Lx3
CHAPTER 8 WATCHDOG TIMER
Remark If the overflow time is set to 2¹⁰/fIL, the window close time and open time are as follows.
Window close time
Window open time
50%
0 to 18.96 ms
18.96 to 31.03 ms
(2.7 V ≤ VDD ≤ 5.5 V)
Setting of Window Open Period
75%
100%
0 to 9.48 ms
None
9.48 to 31.03 ms
0 to 31.03 ms
<When window open period is 50%>
• Overflow time:
2¹⁰/fIL (MAX.) = 2¹⁰/33 kHz (MAX.) = 31.03 ms
• Window close time:
0 to 2¹⁰/fIL (MIN.) × (1 − 0.5) = 0 to 2¹⁰/27 kHz (MIN.) × 0.5 = 0 to 18.96 ms
• Window open time:
2¹⁰/fIL (MIN.) × (1 − 0.5) to 2¹⁰/fIL (MAX.) = 2¹⁰/27 kHz (MIN.) × 0.5 to 2¹⁰/33 kHz (MAX.)
= 18.96 to 31.03 ms
8.4.4 Setting watchdog timer interval interrupt
Depending on the setting of bit 7 (WDTINT) of an option byte (000C0H), an interval interrupt (INTWDTI) can be
generated when 75% of the overflow time is reached.
Table 8-5. Setting of Watchdog Timer Interval Interrupt
WDTINT
0
1
Use of Watchdog Timer Interval Interrupt
Interval interrupt is used.
Interval interrupt is generated when 75% of overflow time is reached.
Caution When operating with the X1 oscillation clock after releasing the STOP mode, the CPU starts
operating after the oscillation stabilization time has elapsed.
Therefore, if the period between the STOP mode release and the watchdog timer overflow is short, an
overflow occurs during the oscillation stabilization time, causing a reset.
Consequently, set the overflow time in consideration of the oscillation stabilization time when
operating with the X1 oscillation clock and when the watchdog timer is to be cleared after the STOP
mode release by an interval interrupt.
Remark The watchdog timer continues counting even after INTWDTI is generated (until ACH is written to the WDTE
register). If ACH is not written to the WDTE register before the overflow time, an internal reset signal is
generated.
R01UH0004EJ0501 Rev.5.01
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Jun 20, 2011