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| 型號： | 22278A1 |
| 英文描述： | 5V EconoReset |
| 中文描述： | 復(fù)位引腳電路的快閃記憶體部門的保護管理 |
| 文件頁數(shù)： | 2/5頁 |
| 文件大?。?/td> | 90K |
| 代理商： | 22278A1 |
Publication#
22278
Issue Date:
April 22, 2003
Rev:
A
Amendment/
1
8-20
Reset Pin Circuitry for Flash Memory Sector
Protection Management
Application Note
This document is intended to assist designers in pro-
viding the necessary circuitry to support in-system sec-
tor protection management, at a low incremental cost.
AMD Sector Protection
All AMD single power supply Flash memories are inter-
nally divided into sections called sectors. Each sector
has a related control bit that can protect a sector by dis-
abling program and erase functions within the address
boundaries of the sector. Most devices can protect any
combination of sectors throughout the device. In a few
devices, each protection control bit manages a group
of sectors such that only groups of sectors can be pro-
tected. In effect, sector protection can change one or
more sectors into ROM type memory that cannot be al-
tered during normal system operation.
High Voltage Controlled Protection
The AMD Flash sector protection bits provide a hard-
ware controlled level of data protection because they
cannot be overridden or modified by software managed
logic level control signals. A “super-voltage,” V
ID
(typi-
cally 11.5 V to 12.5 V), is required to temporarily ignore
or modify the sector protection bits. The super-voltage
is the key used to unlock and allow access to the sector
protection control bits.
Sector protection is often used to safeguard critical por-
tions of stable factory programmed code. This hard-
ware level of protection is secure against data corrup-
tion from viruses or from erroneously written software.
A virus or software error may initiate a valid program or
erase sequence, but without applying the high voltage
key the protected sectors cannot be erased or overwrit-
ten. High voltage controlled data protection is not in-
tended for general purpose in-system use; instead it is
intended to be difficult to defeat. Many systems are de-
signed to exclude the availability of a high voltage
source to the Flash memory in order to ensure that sec-
tor protection is permanent.
Major programming equipment vendors provide the
necessary super-voltage and sector protect routines as
part of their Flash programming support. Flash can be
programmed and protected in one of the many commer-
cially available EEPROM programmers before it is in-
stalled in the system. After the Flash memory is installed,
the protected sectors are safe from any further modifica-
tion or corruption while in the system.
In-System Sector Protection Management
Systems can be designed to allow the option of man-
aging Flash sector protection after the memory is in-
stalled in the system. This approach is useful to allow
memory to be mounted unprogrammed, and to later
download software to the Flash memory and protect crit-
ical sectors during the manufacturing process. It is also
valuable for updating information in the critical sectors
after a system has been shipped to end customers.
For in-system programming or reprogramming, AMD
Flash can be temporarily unprotected by applying V
ID
(11.5 V to 12.5 V) to the RESET# pin. When V
ID
is re-
moved from the RESET# pin, all sectors return to their
previous state of protection. AMD Flash devices with a
process revision letter of B or higher, such as the
29LV800B, also allows the sector protection bits to be
cleared and reprogrammed to protect a different com-
bination of sectors, via software commands while the
device is in the temporary unprotect mode. (See
datasheet sections entitled “Sector Protection/Unpro-
tection” and “Temporary Sector Unprotect” for detailed
instructions concerning modification of protection bits
via software commands.)
To manage sector protection in-system, the designer
must provide: the V
ID
voltage supply, a means of
switching the voltage on and off, and isolation of other
system components while the V
ID
level is placed onto
the RESET# pin.
Method for Providing High Voltage
Isolation to the System Reset
In general, an interface must exist between the system
Reset signal and the RESET# pin of the Flash compo-
nent to reset the internal Flash programming and erase
state machines along with the rest of the system. This
system reset connection is at normal system logic level
voltages. To allow the normal logic level connection to
function and to achieve system isolation from the high
voltage when it is applied to the Flash RESET# pin, a
simple circuit can be added to the design.
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