M32CSLASH8B datasheet(321/406 Pages) RENESAS

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M32C/8B Group

23. Flash Memory

Preliminary specification

Specifications in this manual are tentative and subject to change.

REJ09B0450-0050 Rev.0.50 Oct 31, 2008

Page 304 of 385

23.3

Protect Function

There are two types of protect function. One is to protect data from accidentally erase or program on the flash

memory, which is provided by the lock bit protect function. The other is to prevent the program code from being

leaked to the third party, which is provided by the ROM code protect function and the ID code check function.

23.3.1

Lock bit Protect Function

The lock bit protect function is used in any flash memory rewrite mode. This function provides protection against

erase or program on a block basis. To use the lock bit protect function, set the FMR02 bit in the FMR0 register to 0

(lock bit enabled).

Each block in the flash memory has the lock bit. When the lock bit is set to 0 (locked), the block cannot be erased

nor programmed. To set the lock bit to 0, execute the lock bit program command in the software command.

The FMR31 bit in the FMR3 register determines whether the lock bit status is read via the data bus or by the

FMR16 bit in the FMR1 register. When the lock bit program command is executed, the lock bit status is read via

the data bus if the FMR31 bit is set to 0, or is stored in the FMR16 bit if the FMR31 bit is set to 1.

To disable the lock bit protect function, set the FMR02 bit in the FMR0 register to 1 (lock bit disabled). The

FMR02 bit diables the lock bit protect function without changing the lock bit status. When the FMR02 bit is set to

1, all the blocks can be erased and programmed regardless of the lock bit status. When the block erase command is

executed while the FMR02 bit is set to 1, the lock bit data as well as data in the block are erased and the lock bit

becomes 1 (unlocked).

23.3.2

ROM Code Protect Function

The ROM code protect function is used in parallel I/O mode. This function provides protection against read and

program to all blocks. Each block has two protect bits. Table 23.2 lists addresses of the protect bits. If any of

these protect bits is set to 0 (protected), all blocks becomes protected and the parallel programmer cannot read

nor program to any areas in the flash memory. To set the protect bit to 0, execute the protect bit program

command. To enhance security, set all the protect bits in the flash memory to 0 when using the ROM code

protect function.

The protect bit status is read via the data bus by executing the read protect bit status command.

To disable the ROM code protect function, erase all the blocks whose protect bit is set to 0 by executing the

block erase command. All the protect bits of the erased blocks become 1 (unprotected) and the ROM code

protect function is disabled.

Table 23.2

Address of Protect Bit

Block

Protect bit 1

Protect bit 0

Block B

00E300h

00E100h

Block A

00F300h

00F100h

Block 3

FC0300h

FC0100h

Block 2

FD0300h

FD0100h

Block 1

FE0300h

FE0100h

Block 0

FF0300h

FF0100h

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