M29W017D datasheet(31/36 Pages) STMICROELECTRONICS

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M29W017D

APPENDIX C. BLOCK PROTECTION

Block protection can be used to prevent any oper-

ation 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 Program-

mer technique, the In-System technique and Tem-

porary Unprotection. Temporary Unprotection is

controlled by the Reset/Block Temporary Unpro-

tection pin, RP; this is described in the Signal De-

scriptions 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 tech-

niques for AMD parts will not work on STMicro-

electronics parts. Care should be taken when

changing drivers for one part to work on another.

Programmer Technique

The Programmer technique uses high (VID) volt-

age 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 14,

Programmer Equipment Block Protect Flowchart.

To unprotect the whole chip it is necessary to pro-

tect all of the blocks first, then all blocks can be un-

protected at the same time. To unprotect the chip

follow Figure 15, Programmer Equipment Chip

Unprotect Flowchart. Table 23, Programmer

Technique Bus Operations, 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.

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 micro-

processor bus, therefore this technique is suitable

for use after the Flash has been fitted to the sys-

tem.

To protect a block follow the flowchart in Figure 16,

In-System 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 Fig-

ure 17, In-System 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 pro-

cedure before reaching the end. Chip Unprotect

can take several seconds and a user message

should be provided to show that the operation is

progressing.

Table 23. Programmer Technique Bus Operations, BYTE = VIH or VIL

Operation

Address Inputs

A0-A20

Data Inputs/Outputs

DQ15A–1, DQ14-DQ0

Block Protect

VIL

VID

VIL Pulse

A9 = VID, A12-A20 Block Address

Others = X

Chip Unprotect

VID

VIL Pulse

A9 = VID, A12 = VIH, A15 = VIH

Others = X

Block Protection

Verify

VIL

VIH

A0 = VIL, A1 = VIH, A6 = VIL, A9=VID,

A12-A20 Block Address

Others = X

Pass = XX01h

Retry = XX00h

Block Unprotection

Verify

VIL

VIH

A0 = VIL, A1 = VIH, A6 = VIH, A9 = VID,

A12-A20 Block Address

Others = X

Retry = XX01h

Pass = XX00h

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