M29F800DB datasheet(46/53 Pages) STMICROELECTRONICS

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Block protection

M29F800DT

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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.

9.1

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 = VIH or 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.

9.2

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 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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