M29W640DB datasheet(43/49 Pages) STMICROELECTRONICS

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M29W640DT, M29W640DB

APPENDIX D. BLOCK PROTECTION

Block protection can be used to prevent any oper-

ation from modifying the data stored in the memo-

ry. The blocks are protected in groups, refer to

APPENDIX A., Table 19. and Table 20. for details

of the Protection Groups. Once protected, Pro-

gram 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 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.

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 group of blocks follow the flowchart in

Figure 16., Programmer Equipment Group Protect

Flowchart. To unprotect the whole chip it is neces-

sary to protect all of the groups first, then all

groups can be unprotected at the same time. To

unprotect the chip follow Figure 17., Programmer

Equipment

Chip

Unprotect

Flowchart.

Table

28., Programmer

Technique

Bus

Operations,

BYTE = VIH or VIL, gives a summary of each oper-

ation.

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(1). This can be achieved without violating

the maximum ratings of the components on the mi-

croprocessor bus, therefore this technique is suit-

able for use after the memory has been fitted to

the system.

To protect a group of blocks follow the flowchart in

Figure 18., In-System Equipment Group Protect

Flowchart. To unprotect the whole chip it is neces-

sary to protect all of the groups first, then all the

groups 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 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.

Note: 1. RP can be either at VIH or at VID when using the In-Sys-

tem Technique to protect the Extended Block.

Table 28. Programmer Technique Bus Operations, BYTE = VIH or VIL

Note: 1. Block Protection Groups are shown in APPENDIX A., Tables 19 and 20.

Operation

Address Inputs

A0-A21

Data Inputs/Outputs

DQ15A–1, DQ14-DQ0

Block (Group)

Protect(1)

VIL

VID

VIL Pulse

A9 = VID, A12-A21 Block Address

Others = X

Chip Unprotect

VID

VIL Pulse

A9 = VID, A12 = VIH, A15 = VIH

Others = X

Block (Group)

Protection Verify

VIL

VIH

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

A12-A21 Block Address

Others = X

Pass = XX01h

Retry = XX00h

Block (Group)

Unprotection Verify

VIL

VIH

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

A12-A21 Block Address

Others = X

Retry = XX01h

Pass = XX00h

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