HD6433044 Datasheet, PDF (637/867 Pages) Hitachi Semiconductor – Hitachi Single-Chip Microcomputer

(5) Do not apply 12 V to the V_PP pin during normal operation. To prevent microcontroller errors
caused by accidental programming or erasing, apply 12 V to V_PP only when the flash memory is
programmed or erased, or when flash memory is emulated by RAM. While 12 V is applied, the
watchdog timer should be running and enabled to halt runaway program execution, so that
program runaway will not lead to overprogramming or overerasing.
(6) Disable watchdog-timer reset output (RESO) while the programming voltage (V_PP) is turned
on. If 12 V is applied during watchdog timer reset output (while the RESO pin is low), overcurrent
flow will permanently destroy the reset output circuit. The watchdog timers reset output enable bit
(RSTOE) should not be set to 1.
If a pull-up resistor is externally attached to the V_PP/RESO pin, a diode is necessary to prevent
reverse current from flowing to V_CC when V_PP is applied (figure 18-31).
(7) If the watchdog timer generates a reset output signal when 12 V is not applied, the rise and
fall of the reset output waveform will be delayed by any decoupling capacitors connected to the
V_PP pin.
+5 V
Pull-up resistor and
a diode
+12 V
1.0 µF
V_PP /
RESO
0.01 µF
H8/3048F
Figure 18-31 V_PP Power Supply Circuit Design (Example)
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