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23.7 Flash Security Function
The flash security function can preserve the contents of flash memory.
■
Overview
Writing the protection code, 01
memory. If flash memory is protected once, it is impossible to release the protected condition
until the chip deletion is completed. Unless the protected condition is released, it is impossible
to read/write data of flash memory from an external pin. This function is suitable for the
application which requires security of the self-conclusion-type program and data stored in flash
memory.
The address of a security bit depends on the size of installed flash memory. Table 23.7-1 shows
a list of the flash security bit address.
Table 23.7-1 Flash Security Bit Address
MB90F488B
MB90F489B
■
Setting of security
The security function is set after writing the protection code "01
of the external reset or the power supply.
■
Cancel of security
Execution of the chip deletion
■
Operation in security permission
•
Read : The invalid data is read out from the external pin.
•
Write : Unable to write.
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the others
•
These setting for the general-purpose parallel writer should depend on the specification of
the using parallel writer.
•
It is recommended to write the protection code at the end of flash programming.
The purpose is to prevent from being protected unintentionally during programming.
Note:
A security bit is located within an area of flash memory. Writing the protection code, "01
security bit guarantees security. Therefore, do not write "01
security function.
For the address of a security bit, see Table 23.7-1 mentioned above.
, to the security bit of flash memory can limit access to flash
H
Flash memory size
built-in 2M bits flash memory
built-in 3M bits flash memory
CHAPTER 23 2M/3M BIT FLASH MEMORY
Security bit address
FC0001
" to a security bit and resumption
H
" to this address when not using the
H
H
F90001
H
", to a
H
503
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