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M29DW640F
Block protection
Appendix D
Block protection
Block protection can be used to prevent any operation from modifying the data stored in the
Protection Groups. Once protected, Program and Erase operations within the protected
group fail to change the data.
There are three techniques that can be used to control Block Protection, these are the
Programmer technique, the In-System technique and Temporary Unprotection. Temporary
Unprotection is controlled by the Reset/Block Temporary Unprotection pin, RP; this is
described in the Signal Descriptions section.
To protect the Extended Block issue the Enter Extended Block command and then use
either the Programmer or In-System technique. Once protected issue the Exit Extended
Block command to return to read mode. The Extended Block protection is irreversible, once
protected the protection cannot be undone.
D.1
Programmer technique
The Programmer technique uses high (VID) voltage levels on some of the bus pins. These
cannot be achieved using a standard microprocessor bus, therefore the technique is
recommended only for use in Programming Equipment.
Protect flowchart. To unprotect the whole chip it is necessary to protect all of the groups first,
then all groups can be unprotected at the same time. To unprotect the chip follow
Figure 21:The timing on these flowcharts is critical. Care should be taken to ensure that, where a
pause is specified, it is followed as closely as possible. Do not abort the procedure before
reaching the end. Chip Unprotect can take several seconds and a user message should be
provided to show that the operation is progressing.
D.2
In-System technique
The In-System technique requires a high voltage level on the Reset/Blocks Temporary
Unprotect pin, RP (1). This can be achieved without violating the maximum ratings of the
components on the microprocessor bus, therefore this technique is suitable for use after the
memory has been fitted to the system.
Protect flowchart. To unprotect the whole chip it is necessary to protect all of the groups first,
then all the groups can be unprotected at the same time. To unprotect the chip follow
The timing on these flowcharts is critical. Care should be taken to ensure that, where a
pause is specified, it is followed as closely as possible. Do not allow the microprocessor to
service interrupts that will upset the timing and do not abort the procedure before reaching
the end. Chip Unprotect can take several seconds and a user message should be provided
to show that the operation is progressing.