M29F016D datasheet(31/37 Pages) STMICROELECTRONICS

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M29F016D

APPENDIX C. 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 17 for details of the Protection

Groups. Once protected, Program and Erase op-

erations 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.

To protect the Extended Block issue the Enter Ex-

tended Block command and then use either the

Programmer or In-System technique. Once pro-

tected issue the Exit Extended Block command to

return to read mode. The Extended Block protec-

tion is irreversible, once protected the protection

cannot be undone.

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 Block 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 24,

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 memory has been fitted to the sys-

tem.

To protect a group of blocks follow the flowchart in

Figure 18, In-System Block Protect Flowchart. To

unprotect the whole chip it is necessary 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 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 24. Programmer Technique Bus Operations, BYTE = VIH or VIL

Note: 1. Block Protection Groups are shown in Appendix A, Table 17.

Operation

Address Inputs

A0-A20

Data Inputs/Outputs

DQ15A–1, DQ14-DQ0

Block (Group)

Protect(1)

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 (Group)

Protection Verify

VIL

VIH

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

A12-A20 Block Address

Others = X

Pass = XX01h

Retry = XX00h

Block (Group)

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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