M29W400DT, M29W400DB
Block protection
Appendix B
Block protection
Block protection can be used to prevent any operation from modifying the data stored in the
Flash. Each block can be protected individually. Once protected, Program and Erase
operations on the block 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 Section 2: Signal descriptions.
Unlike the command interface of the Program/Erase controller, the techniques for protecting
and unprotecting blocks change between different Flash memory suppliers. For example,
the techniques for AMD parts will not work on Numonyx parts. Care should be taken when
changing drivers for one part to work on another.
B.1
Programmer technique
The programmer technique uses high (V ) voltage levels on some of the bus pins. These
ID
cannot be achieved using a standard microprocessor bus, therefore the technique is
recommended only for use in programming equipment.
To protect a block follow the flowchart in Figure 19: Programmer equipment block protect
flowchart. To unprotect the whole chip it is necessary to protect all of the blocks first, then all
blocks can be unprotected at the same time. To unprotect the chip follow Figure 20:
Programmer equipment chip unprotect flowchart. Table 23: Programmer technique bus
operations, BYTE = V or V , gives a summary of each operation.
IH
IL
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.
B.2
In-system technique
The in-system technique requires a high voltage level on the Reset/Blocks Temporary
Unprotect pin, RP. 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
Flash has been fitted to the system.
To protect a block follow the flowchart in Figure 21: In-system equipment block protect
flowchart. To unprotect the whole chip it is necessary to protect all of the blocks first, then all
the blocks can be unprotected at the same time. To unprotect the chip follow Figure 22: In-
system equipment chip unprotect flowchart.
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.
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NUMONYX [ NUMONYX B.V ]
