P R E L I M I N A R Y
(ACC) and unlock bypass functions are not available
SecSi (Secured Silicon) Sector Flash
Memory Region
when programming the SecSi Sector.
The SecSi Sector area can be protected using one of
the following procedures:
The SecSi (Secured Silicon) Sector feature provides a
Flash memory region that enables permanent part
identification through an Electronic Serial Number
(ESN). The SecSi Sector uses a SecSi Sector Indica-
tor Bit to indicate whether or not the SecSi Sector is
locked when shipped from the factory. This bit is per-
manently set at the factory and cannot be changed,
which prevents cloning of a factory locked part. This
ensures the security of the ESN once the product is
shipped to the field.
■ Write the three-cycle Enter SecSi Sector Region
command sequence, and then follow the in-system
sector protect algorithm as shown in Figure 2, ex-
cept that RESET# may be at either VIH or VID. This
allows in-system protection of the without raising
any device pin to a high voltage. Note that this
method is only applicable to the SecSi Sector.
■ Write the three-cycle Enter SecSi Sector Region
command sequence, and then use the alternate
method of sector protection described in the “Au-
toselect Mode”.
AMD offers the device with the SecSi Sector either
factory locked or customer lockable. The fac-
tory-locked version is always protected when shipped
from the factory, and has the SecSi Sector Indicator
Bit permanently set to a “1.” The customer-lockable
version is shipped with the unprotected, allowing cus-
tomers to utilize the that sector in any manner they
choose. The customer-lockable version has the SecSi
Sector Indicator Bit permanently set to a “0.” Thus, the
SecSi Sector Indicator Bit prevents customer-lockable
devices from being used to replace devices that are
factory locked.
Once the SecSi Sector is locked and verified, the sys-
tem must write the Exit SecSi Sector Region
command sequence to return to reading and writing
the remainder of the array.
The SecSi Sector protection must be used with cau-
tion since, once protected, there is no procedure
available for unprotecting the SecSi Sector area and
none of the bits in the SecSi Sector memory space
can be modified in any way.
The system accesses the SecSi Sector through a
command sequence (see “Enter SecSi Sector/Exit
SecSi Sector Command Sequence”). After the system
has written the Enter SecSi Sector command se-
quence, it may read the SecSi Sector by using the
addresses normally occupied by the boot sectors. This
mode of operation continues until the system issues
the Exit SecSi Sector command sequence, or until
power is removed from the device. On power-up, or
following a hardware reset, the device reverts to send-
ing commands to the boot sectors.
Hardware Data Protection
The command sequence requirement of unlock cycles
for programming or erasing provides data protection
against inadvertent writes (refer to Tables 15 and 16
for command definitions). In addition, the following
hardware data protection measures prevent accidental
erasure or programming, which might otherwise be
caused by spurious system level signals during VCC
power-up and power-down transitions, or from system
noise.
Factory Locked: SecSi Sector Programmed and
Protected At the Factory
Low VCC Write Inhibit
When VCC is less than VLKO, the device does not ac-
cept any write cycles. This protects data during VCC
power-up and power-down. The command register
and all internal program/erase circuits are disabled,
and the device resets to reading array data. Subse-
In a factory locked device, the SecSi Sector is pro-
tected when the device is shipped from the factory.
The SecSi Sector cannot be modified in any way. The
device is available preprogrammed with a random, se-
cure ESN only.
quent writes are ignored until VCC is greater than VLKO
.
In the Top Boot device the ESN will be at addresses
1FF000h–1FF007h in word mode (or addresses
3FE000h–3FE00Fh in byte mode).
The system must provide the proper signals to the
control pins to prevent unintentional writes when VCC
is greater than VLKO
.
Customer Lockable: SecSi Sector NOT
Programmed or Protected At the Factory
Write Pulse “Glitch” Protection
Noise pulses of less than 5 ns (typical) on OE#, CE#f
or WE# do not initiate a write cycle.
If the security feature is not required, the SecSi Sector
can be treated as an additional Flash memory space,
expanding the size of the available Flash array. The
SecSi Sector can be read any number of times, but
can be programmed and locked only once, and cannot
be erased. Note that the accelerated programming
Logical Inhibit
Write cycles are inhibited by holding any one of OE# =
VIL, CE#f = VIH or WE# = VIH. To initiate a write cycle,
22
Am49DL32xBG
July 19, 2002
CYPRESS [ CYPRESS ]
