M29W160EB View Datasheet(PDF) - STMicroelectronics
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M29W160EB Datasheet PDF : 40 Pages
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M29W160ET, M29W160EB
APPENDIX C. BLOCK PROTECTION
Block protection can be used to prevent any oper-
ation from modifying the data stored in the Flash
memory. 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 could change between differ-
ent Flash memory suppliers.
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 17,
Programmer Equipment Block Protect Flowchart.
During the Block Protect algorithm, the A19-A12
Address Inputs indicate the address of the block to
be protected. The block will be correctly protected
only if A19-A12 remain valid and stable, and if
Chip Enable is kept Low, VIL, all along the Protect
and Verify phases.
The Chip Unprotect algorithm is used to unprotect
all the memory blocks at the same time. This algo-
rithm can only be used if all of the blocks are pro-
tected first. To unprotect the chip follow Figure 18,
Programmer Equipment Chip Unprotect Flow-
chart. Table 27, Programmer Technique Bus Op-
erations, 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 memory has been fitted to
the system.
To protect a block follow the flowchart in Figure 19,
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 20, 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 27. Programmer Technique Bus Operations, BYTE = VIH or VIL
Operation
EG
W
Address Inputs
A0-A19
Block Protect
VIL VID VIL Pulse
A9 = VID, A12-A19 Block Address
Others = X
Chip Unprotect
VID VID VIL Pulse
A9 = VID, A12 = VIH, A15 = VIH
Others = X
Block Protection
Verify
VIL VIL
A0 = VIL, A1 = VIH, A6 = VIL, A9 = VID,
VIH
A12-A19 Block Address
Others = X
Block Unprotection
Verify
VIL VIL
A0 = VIL, A1 = VIH, A6 = VIH, A9 = VID,
VIH
A12-A19 Block Address
Others = X
Data Inputs/Outputs
DQ15A–1, DQ14-DQ0
X
X
Pass = XX01h
Retry = XX00h
Retry = XX01h
Pass = XX00h
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