HD64F3437TF16 Datasheet, PDF (460/752 Pages) Hitachi Semiconductor – 12 V must not be applied to the S-mask model (single-power-supply specification), as this may permanently damage the device.

t_OSC1
ø
2.7 to 5.5 V^*
V_CC
12 ± 0.6 V
V_CC + 2 V to 11.4 V
V_PP
V_CCV
Boot mode
12 ± 0.6 V
V_PP
User program
mode
V_CCV
0 µs min
0 µs min
0 µs min
Timing at which boot
program branches
to RAM area
0 to V_CCV
0 to V_CCV
RES
Periods during which the V_PP flag is being set or
cleared and flash memory must not be accessed
Min 10ø
(when RES is low)
Note: * In the LH version, V_CC = 3.0 V to 5.5 V.
Figure 19.20 V_PP Power-On and Power-Off Timing
(6) Do not apply 12 V to the FV_PP pin during normal operation.
To prevent accidental programming or erasing due to microcontroller program runaway etc., apply
12 V to the V_PP pin only when the flash memory is programmed or erased, or when flash memory
is emulated by RAM. Overprogramming or overerasing due to program runaway can cause
memory cells to malfunction. Avoid system configurations in which 12 V is always applied to the
FV_PP pin.
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.
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