High Voltage Sector Protect AN e

High Voltage Sector Protect AN e
Spansion® High Voltage Sector Group
Protection / Un-Protection
Application Note
1. Sector Protection
Each Spansion flash memory array is portioned into one or more banks and further subdivided into sections
called sectors. For the following discussion, the term sector applies to both boot sectors and sector groups. A
sector group consists of two or more adjacent sectors that are protected or unprotected at the same time.
Reference respective flash data sheet to find details for that device's sector block grouping.
Each sector has control bits that can protect a sector by disabling program and erase functions within the
address boundaries of the sector. Most devices can protect a combination of sectors which comprise the
flash array. Flash devices use a control bit to manage the protection of individual sectors or a group of
sectors. From the user perspective the sector protection can change one or more sectors into ROM type
memory that cannot be altered during normal operation.
Spansion flash can use High Voltage Protection or Advanced Sector Protection to invoke the subject sector
protection depending on the flash family. This document highlights the High Voltage Sector Group Protection/
Unprotection feature supported by Spansion S29AL-J, S9AL-J, and S29JL-J flash families, including the
necessary circuitry to support in-system sector protection management.
2. High Voltage Controlled Sector Group Protection
Sector protection is often used to safeguard critical portions the flash memory map such as boot / application
code or critical data areas. The High Voltage Controlled Sector Group Protection Is a hardware based
protection setup that secures the subject sector(s) against data corruptions such as from viruses or an
erroneous flash access. This high voltage hardware sector group protection feature disables both program
and erases operations in the specified sector group(s). The hardware sector group un-protection feature
re-enables both program and erase operations in a once protected sector group. The Spansion High Voltage
Controlled Sector Group Protection uses the high-voltage VID applied to RESET# as a key used to access the
sector protection control bits.
Figure 2.1 provides an example of the S29AL-J Sector protection and un-protection algorithms; these
algorithms highlight the steps necessary to complete the respective sector protect or unprotect process.
Please note prior to completing a sector group unprotect, all unprotected sector groups must first be
protected prior to the first sector group unprotect write cycle. Spansion flash ships all standard flash devices
with sector groups in the unprotected state.
Please reference the respective data sheet to obtain the subject devices complete algorithms and timing
diagrams. In cases where a module or system design does not support a high voltage source to the flash
memory; flash can be pre-programmed and protected using many commercially available flash programmers
prior to installing the flash in the system module.
Publication Number High_Voltage_Sector_Protect_AN
Revision 01
Issue Date October 28, 2011
A pplication
Note
Figure 2.1 High Voltage Protection Algorithm
START
Protect all sectors:
The indicated portion
of the sector group protect
algorithm must be
performed for all
unprotected sector groups
prior to issuing the
first sector group
unprotect address
START
PLSCNT = 1
RESET# = VID
Wait 1 ms
Temporary Sector
Group Unprotect Mode
No
PLSCNT = 1
RESET# = VID
Wait 1 ms
No
First Write
Cycle = 60h?
First Write
Cycle = 60h?
Yes
No
Yes
All sectors
protected?
Set up sector
group address
Yes
Set up first sector
group address
Sector Group Protect:
Write 60h to sector group
address with
A6 = 0,
A3 = A2 = 0,
A1 = 1, A0 = 0
Sector Group Unprotect:
Write 60h to sector
address with
A6 = 1,
A3 = A2 = 0,
A1 = 1, A0 = 0
Wait 150 µs
Increment
PLSCNT
Verify Sector Group
Protect: Write 40h
to sector group address
with A6 = 0,
A3 = A2 = 0,
A1 = 1, A0 = 0
Read from
sector group address
with A6 = 0,
A3 = A2 = 0,
A1 = 1, A0 = 0
Wait 1.5 ms
Reset
PLSCNT = 1
Increment
PLSCNT
No
Yes
Device failed
Verify Sector Group
Unprotect: Write
40h to sector group
address with
A6 = 1,
A3 = A2 = 0,
A1 = 1, A0 = 0
Read from
sector group address
with A6 = 1,
A3 = A2 = 0,
A1 = 1, A0 = 0
No
PLSCNT
= 25?
Temporary Sector
Group Unprotect Mode
Data = 01h?
No
Yes
Protect another
sector group?
Yes
PLSCNT
= 1000?
Yes
No
Remove VID
from RESET#
Device failed
No
Data = 00h?
Set up
next sector group
address
Yes
Last sector
No
group verified?
Yes
Write reset
command
Sector Group
Protect Algorithm
Sector Group
Unprotect Algorithm
Sector Group
Protect complete
Remove VID
from RESET#
Write reset
command
Sector Group
Unprotect complete
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App l ic atio n
3.
No t e
In-System Sector Protection Management
Spansion High Voltage Controlled Sector Group Protection allows management of the flash sector protection
after the flash device is mounted on the system module. In such cases, there must be a module or system
design provision to support the high voltage VID flash input requirements. This approach provides the option
for memory to perform post assembly flash programming followed by sector protection later in the
manufacturing processes. This type of configuration can also provide an option for updating software in the
critical sectors after unit has been shipped to end customers. For in-system programming or reprogramming,
Spansion flash can be temporarily unprotected by applying VID (11.5V to 12.5V) to the RESET# pin. When
VID is removed from the RESET# pin, all sectors return to their previous state of protection. The flash families
S29AL, S29AS, S29JL, and AM29F series allow the sector protection bits to be cleared and reprogrammed to
protect a different combination of sectors, via software commands while the device is in the temporary
unprotect mode. (See the respective data sheet sections entitled “Sector Protection / Un-protection” and
“Temporary Sector Unprotect” for additional details.)
4. Method for Providing High Voltage Isolation to the System Reset
Spansion recommends that a design employ an interface between the system Reset signal and the RESET#
pin of the flash. The RESET# input enables appropriate control to the flash State Machine during power up
and power down, along with the rest of the system. This system reset uses standard logic levels as specified
in the subject data sheet. To address the situation where the high voltage VID is applied to the flash RESET#
pin, a small circuit can be added to the design. This circuit configuration enables the normal logic level inputs
to function and to achieve system isolation from the high voltage VID when applied. Figure 4.1 shows the use
of series resistor between the RESET# pin and the system level Reset signal along with a Schottky diode
between the system reset and the system VCC.
Figure 4.1 RESET# Pin Isolation Circuitry
+12V
10 kW
System RESET
Flash RESET# Pin
Schottky
Diode
VCC (3V or 5V)
When VID is not connected to the flash RESET# pin, the series resistor allows the normal logic level on the
system reset to propagate to the flash memory. The flash RESET# pin is low capacitance, and in combination
with the added resistor, the rise time of the reset signal is still typically <300 ns. The normal flash reset
functionality is not hindered by the series resistor. When high voltage is applied to the RESET# pin, the
resistor limits current flow to the system reset signal. The maximum current flow to the system reset (when
the system asserts VIL on the system reset signal) is 1.2 mA. The Schottky diode guarantees a clamp on the
system reset signal to no more than VCC + ~0.3V. ESD protection diodes already built into the inputs of other
devices attached to the system reset signal could serve a similar purpose, but the typical 0.7V voltage rise
induced by these diodes would clamp the voltage to a level which exceeds the VIH max data sheet parameter.
Use of a Schottky diode clamp provides a means not to exceed the VIH parameter. The resistor and diode
combination form the isolation circuitry and present very minimal additional system cost while enabling the
flexibility of in-system sector protection management.
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3
A pplication
5.
Note
Methods for Providing High Voltage to the Flash Device RESET# Pin
The flash RESET# is a high impedance input and does not the VID signal to provide significant current; the
voltage level is detected by the flash input. The rise and fall time, when transitioning between normal logic
signal voltage levels and VID, must be limited to tVIDR (500 ns) minimum. There must also be a delay of tRSP
(4 µs) after VID is reached before any writing to the flash memory is begun.
Some systems do not have 12V available, but can provide a 12V supply from an outside source such as a
manufacturing test system, daughter card, debug system, or via an external cable or connection. Such an
external supply may only be available at a factory or service center location. This method is the simplest in
that only a connection to the flash RESET# pin needs to be provided. The voltage source and method for
switching it on and off are external to the system being programmed. The system carries no burden of extra
circuitry to create and control the high voltage. This approach also ensures that there is no way for the system
to accidentally switch on the unlock voltage; without the external voltage supply to override sector protection.
For systems where a 12V source is available, it may be desirable to allow the 12V supply to be switched to
the flash RESET# pin within the system. One suggestion for switching the VID level is shown in Figure 5.1. By
placing a P-channel MOSFET between the VID source and the flash RESET# pin. The gate of the P-channel
MOSFET is pulled up to VID through a 100 k resistor. The gate of the P-channel device can be pulled down
to ground by a TTL logic level controlled N-channel MOSFET. Depending on the operational characteristics of
the P-channel MOSFET, and the characteristics of the RV Control signal, the gate voltage may require
conditioning using a 5K and 100 pF RC circuit. This allows the turn on and off delay of the P-channel to
ensure that the rise and fall time of VID is 500 ns. The gate of the logic level N-channel MOSFET is driven by
a system control signal to enable the sector protection unlock voltage. A 100 K resistor from the VID source
to VCC is recommended for situations where the VID supply is not always connected (or not always active) to
keep the MOSFETs properly biased.
Figure 5.1 VID Routing Circuitry
+12V
100 kW
VCC
100 kW
100 kW
RV
Control
System
RESET
10 kW
RESET# Pin
Schottky
Diode
VCC
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October 28, 2011
App l ic atio n
No t e
Spansion High Voltage Sector Group Protection / Un-protection also supports a “Temporary Sector Group
Unprotect” feature allowing the temporary un-protection of previously protected sector groups to change data
in-system. The Sector Group Unprotect mode is activated by setting the RESET# pin to VID. During this
mode, formerly protected sector groups can be programmed or erased by selecting the sector group
addresses. Once VID is removed from the RESET# pin, all the previously protected sector groups are
protected again. Reference Figure 5.2 to see S29AL016 example of the Temporary Sector Group Unprotect
Operation.
Figure 5.2 Temporary Sector Group Unprotect Operation
Start
RESET# = VID
(Note 1)
Perform Erase or
Program Operations
RESET# = VIH
Temporary Sector Group
Unprotect Completed
(Note 2)
Notes:
1. All protected sector unprotected. (If WP# = VIL, the highest or lowest address sector remains protected for uniform sector devices; the top
or bottom two address sectors remains protected for boot sector devices).
2. All previously protected sector groups are protected once again.
6. Conclusion
Spansion NOR flash memory array is partitioned into one or more banks and further subdivided into sections
called sectors. Spansion provides a high voltage sector group protection/un-protection feature to enable a
designer the option to protect selected area in the flash memory array from inadvertent erasure or
programming. This high voltage sector group protection/un-protection feature requires the application of
super-voltage VID to the flash RESET# while executing the sector group protection or un-protection algorithm.
This application note highlighted that high voltage sector group protection / un-protection feature can be used
during programming on commercial programming equipment or via in-system with appropriate system design
considerations.
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A pplication
Note
7. Revision History
Section
Description
Revision 01 (October 28, 2011)
Initial release
6
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October 28, 2011
App l ic atio n
No t e
Colophon
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