M29W640GH, M29W640GL, M29W640GT, M29W640GB
Block Protection
Appendix D
Block Protection
Block protection can be used to prevent any operation from modifying the data stored in the
memory. The blocks are protected in groups, refer to
and
for details of 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.
D.1
Programmer Technique
The Programmer technique uses high (V
ID
) 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.
To protect a group of blocks follow the flowchart in
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
, gives a summary of each operation.
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.
To protect a group of blocks follow the flowchart in
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.
Note:
RP can be either at V
IH
or at V
ID
when using the In-System Technique to protect the
Extended Block.
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NUMONYX [ NUMONYX B.V ]
