HD64F3437TF16 Datasheet, PDF (533/752 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.

Bits 1 and 0—Mode Select 1 and 0 (MDS1, MDS0): These bits indicate the input levels at mode
pins MD₁ and MD₀ (the current operating mode). Bits MDS1 and MDS0 correspond to pins MD₁
and MD₀, respectively. MDS1 and MDS0 are read-only bits, and cannot be modified. The mode
pin (MD₁ and MD₀) input levels are latched into these bits when MDCR is read.
21.1.7 Flash Memory Operating Modes
Mode Transition Diagram: When the mode pins are set in the reset state and a reset start is
effected, the microcontroller enters one of the operating modes as shown in figure 21.2. In user
mode, the flash memory can be read but cannot be programmed or erased.
Modes in which the flash memory can be programmed and erased are boot mode, user
programming mode, and writer mode.
MD₁ = 1
Reset state
User mode
with on-chip ROM
enabled
FLSHE = 1 ^{FLSHE = 0}
RES = 0
RES = 0
*1
User
programming
mode
*2
RES = 0
RES = 0
Writer mode
On-board programming mode
Boot mode
Notes: Transitions between user mode and user programming mode should only be made when the CPU is
not accessing the flash memory.
*1 MD₀ = MD₁ = 0, P92 = P91 = P90 = 1
*2 MD₀ = MD₁ = 0, P92 = 0, P91 = P90 = 1
Figure 21.2 Flash Memory Related State Transitions
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