HD64F3437TF16 Datasheet, PDF(503/752 Page) Hitachi Semiconductor – 12 V must not be applied to the S-mask model (single-power-supply specification), as this may permanently damage the device.

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HD64F3437TF16 Datasheet, PDF (503/752 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.

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20.4.7 Prewrite Verify Mode

Prewrite-verify mode is a verify mode used when programming all bits to equalize their threshold

voltages before erasing them.

To program all bits, follow the prewrite algorithm shown in figure 20.10. The procedure is to

program all flash memory data to H'00 by using H'00 write data. H'00 should also be written when

using RAM for flash memory emulation (when prewriting a RAM area). (This also applies when

using RAM to emulate flash memory erasing with an emulator or other support tool.) After the

necessary programming time has elapsed, exit program mode (by clearing the P bit to 0) and select

prewrite-verify mode (leave the P, E, PV, and EV bits all cleared to 0). In prewrite-verify mode, a

prewrite-verify voltage is applied to the memory cells at the read address. If the flash memory is

read in this state, the data at the read address will be read. After selecting prewrite-verify mode,

wait 4 Âµs or more before reading.

Note: For a sample prewriting program, see the prewrite subroutine in the sample erasing

program.

20.4.8 Protect Modes

Flash memory can be protected from programming and erasing by software or hardware methods.

These two protection modes are described below.

Software Protection: Prevents transitions to program mode and erase mode even if the P or E bit

is set in the flash memory control register (FLMCR). Details are as follows.

Function

Protection Description

Program Erase

Verify*1

Block

protect

Individual blocks can be protected from erasing

and programming by the erase block registers

(EBR1 and EBR2). If H'00 is set in EBR1 and

EBR2, all blocks are protected from erasing and

programming.

Disabled

Disabled Enabled

Emulation

protect*2

When the RAMS or RAM0 bit, but not both,

is set in the wait-state control register (WSCR),

all blocks are protected from programming and

erasing

Disabled

Disabled*3 Enabled

Notes: *1 Three modes: program-verify, erase-verify, and prewrite-verify.

*2 Except in RAM areas overlapped onto flash memory.

*3 All blocks are erase-disabled. It is not possible to specify individual blocks.

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