March 8, 2002 Am49DL640BG 21
PRELIMINARY
SecSi™ (Secured Silicon) Sector
Flash Memory Region
The SecSi (Secured Sili con) Sector feature provides a
Flash memory region that enables permanent part
identification through an Electronic Serial Number
(ESN). The SecSi Sector is 256 bytes in length, and
uses a SecSi Sec tor Indicator Bit (DQ7) to indicate
whether or not the SecSi Sector is locked when
shipped from the factory. This bit is permanently set at
the factory and cann ot be chang ed, which prevents
cloning of a fact ory locked part. Thi s ensures the secu-
rity of the ES N onc e the product is s hipped to the field.
AMD offers th e device with the SecSi Sector e ither
factory locked or customer lockable. The fac-
tory-locked version is always protected when shipped
from the f actor y, and h as the S ecSi (Se cured Silic on)
Sector Indicator Bit permanently set to a “1.” The cus-
tomer-lockable version is shipped with the SecSi Sec-
tor unp rot ected, a llow ing cu stome rs to utilize the th at
sector in any manner they choose. T he customer-lock-
able v ersion has the SecSi (Secured Silicon) Sector
Indicator Bit permanently set to a “0.” Thus, the SecSi
Sector Indicator Bit prevents customer-lockable de-
vices from being used to replace devices that are fac-
tory locked.
The system accesses the SecSi Sector Secure
through a command sequence (see “Enter SecSi™
Sector/Exit S ecSi Sector Command Sequence”). After
the system has writte n t he Enter Se cSi Sector com-
mand sequence, it may read the SecSi Sector by
using the addresses nor mally occupie d by the boot
sectors. This mode of operation continues until the
system issues the Exit SecSi Sector command se-
quence, or until power is removed from the device. On
power-up, or following a hardware reset, the device re-
verts to sending commands to the first 256 bytes of
Sector 0.
Factory Locked: SecSi Sector Programmed and
Protected At the Factory
In a fa ctory locked device, the SecSi Sec tor is pro-
tected when the d evice is sh ipped from the factory.
The SecSi Sector cannot be modified in any way. The
device is preprogrammed with both a random number
and a secure ESN. The 8-word random num ber will at
addresses 000000h–000007h in word mode (or
000000h –00000Fh in byte mode). The secur e ESN
will be pr ogram med in the nex t 8 wo rds at a ddresses
00000 8h–00000Fh (or 000010h–000020h in byte
mode). The device is available preprogrammed with
one of the following:
■ A random, secure ESN only
■ Custome r code through the ExpressFlash service
■ Both a random, secure ESN and customer code
through the ExpressFlash se rvice.
Customers may opt to have their code programmed by
AMD through the AMD E xpressFlas h service. AM D
programs the cus tomer’s cod e, with or without the ran-
dom ESN. Th e de vices ar e then s hipped f rom AMD’s
factory with the SecSi Sector permanently locked.
Contact an AMD representative for details on using
AMD’s ExpressFlash servi ce.
Customer Lockable: SecSi Sector NOT
Programmed or Protected At t he Factory
If the security feature is not required, the SecSi Sector
can be treated a s an additiona l Flash mem ory space .
The SecSi Sector can be read any number of times,
but can be programmed and locked only once. Note
that the accelerated programming (ACC) and unlock
bypass functions are not available when programming
the SecSi Sector.
The SecSi Sector area can be pro tected using one of
the following procedures:
■ 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 RE SET# may be at either V
IH
or V
ID
. Thi s
allows in-sy stem protection of the SecSi Sector Re-
gion 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 Secure
Region command sequence, and then use the alter-
nate method of sector protection described in the
“Sector/Sector Block Protection and Unprotection”
section.
Once the SecSi Sector is locked and verified, the sys-
tem must write the Exit SecSi Sector Region com-
mand sequence to return to reading and writing the
remainder of the array.
The SecSi Sector lock must be used with caution
since, once locked, there is no procedure available for
unlo cking the SecS i Sec tor ar ea an d none of the b its
in the SecSi Sector memory space can be m odified in
any way.
Hardware Data Protection
The command sequence requirement of unlock cycles
for programming or erasing provides data protection
against inadvertent writes (refer to Table 12 for com-
man d def initio ns). I n ad ditio n, th e follow ing hard ware
dat a pr otec tion mea sur es pre vent ac ciden tal er asu re
or programming, which mi ght otherwise be caused by
spurious system level signals during V
CC
power-up
and power-down transitions, or from system noise.
Low V
CC
Wr ite Inhi bit
When V
CC
is less than V
LKO
, the d evic e does no t ac -
cept any write cycles. This protects data during V
CC
