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M29W320DT Datasheet(PDF) 48 Page - STMicroelectronics

Part No. M29W320DT
Description  32 Mbit 4Mb x8 or 2Mb x16, Boot Block 3V Supply Flash Memory
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Maker  STMICROELECTRONICS [STMicroelectronics]
Homepage  http://www.st.com
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M29W320DT Datasheet(HTML) 48 Page - STMicroelectronics

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Block Protection
M29W320DT, M29W320DB
48/56
Appendix C
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 Signal Descriptions section.
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 STMicroelectronics parts. Care
should be taken when changing drivers for one part to work on another.
C.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.
To protect a block follow the flowchart in Figure 16: 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 17:
Programmer Equipment Chip Unprotect Flowchart. Table 27: Programmer Technique Bus
Operations, BYTE = VIHor VIL, 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.
C.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 18: 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
Figure 19: 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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