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參數(shù)資料
| 型號： | AM29PL142DC |
| 英文描述： | 10MS, 8 SOIC, IND TEMP, 1.8V(SERIAL EE) |
| 中文描述： | 用戶可編程ASIC的特殊功能 |
| 文件頁數(shù)： | 27/67頁 |
| 文件大?。?/td> | 635K |
| 代理商： | AM29PL142DC |
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August 8, 2003
Am29PDL129H
25
P R E L I M I N A R Y
so-called
Dynamic Locked or Unlocked
states. They
are called dynamic states because it is very easy to
switch back and forth between the protected and un-
protected conditions. This allows software to easily
protect sectors against inadvertent changes yet does
not prevent the easy removal of protection when
changes are needed. The DYBs maybe set or cleared
as often as needed.
The PPBs allow for a more static, and difficult to
change, level of protection. The PPBs retain their state
across power cycles because they are non-volatile. In-
dividual PPBs are set with a command but must all be
cleared as a group through a complex sequence of
program and erasing commands. The PPBs are also
limited to 100 erase cycles.
The PPB Lock bit adds an additional level of protec-
tion. Once all PPBs are programmed to the desired
settings, the PPB Lock may be set to “1”. Setting the
PPB Lock disables all program and erase commands
to the non-volatile PPBs. In effect, the PPB Lock Bit
locks the PPBs into their current state. The only way to
clear the PPB Lock is to go through a power cycle.
System boot code can determine if any changes to the
PPB are needed; for example, to allow new system
code to be downloaded. If no changes are needed
then the boot code can set the PPB Lock to disable
any further changes to the PPBs during system opera-
tion.
The WP#/ACC write protect pin adds a final level of
hardware protection to sectors SA1-133, SA1-134,
SA2-0 and SA2-1. When this pin is low it is not possi-
ble to change the contents of these sectors. These
sectors generally hold system boot code. The
WP#/ACC pin can prevent any changes to the boot
code that could override the choices made while set-
ting up sector protection during system initialization.
It is possible to have sectors that have been persis-
tently locked, and sectors that are left in the dynamic
state. The sectors in the dynamic state are all unpro-
tected. If there is a need to protect some of them, a
simple DYB Write command sequence is all that is
necessary. The DYB write command for the dynamic
sectors switch the DYBs to signify protected and un-
protected, respectively. If there is a need to change
the status of the persistently locked sectors, a few
more steps are required. First, the PPB Lock bit must
be disabled by either putting the device through a
power-cycle, or hardware reset. The PPBs can then
be changed to reflect the desired settings. Setting the
PPB lock bit once again will lock the PPBs, and the
device operates normally again.
The best protection is achieved by executing the PPB
lock bit set command early in the boot code, and pro-
tect the boot code by holding WP#/ACC = V
IL
.
Table 9.
Sector Protection Schemes
Table 9 contains all possible combinations of the DYB,
PPB, and PPB lock relating to the status of the sector.
In summary, if the PPB is set, and the PPB lock is set,
the sector is protected and the protection can not be
removed until the next power cycle clears the PPB
lock. If the PPB is cleared, the sector can be dynami-
cally locked or unlocked. The DYB then controls
whether or not the sector is protected or unprotected.
If the user attempts to program or erase a protected
sector, the device ignores the command and returns to
read mode. A program command to a protected sector
enables status polling for approximately 1 μs before
the device returns to read mode without having modi-
fied the contents of the protected sector. An erase
command to a protected sector enables status polling
for approximately 50 μs after which the device returns
to read mode without having erased the protected sec-
tor.
The programming of the DYB, PPB, and PPB lock for
a given sector can be verified by writing a
DYB/PPB/PPB lock verify command to the device.
Persistent Sector Protection Mode Locking Bit
Like the password mode locking bit, a Persistent Sec-
tor Protection mode locking bit exists to guarantee that
the device remain in software sector protection. Once
set, the Persistent Sector Protection locking bit pre-
vents programming of the password protection mode
locking bit. This guarantees that a hacker could not
place the device in password protection mode.
Password Protection Mode
The Password Sector Protection Mode method allows
an even higher level of security than the Persistent
Sector Protection Mode. There are two main differ-
ences between the Persistent Sector Protection and
the Password Sector Protection Mode:
DYB
PPB
PPB
Lock
Sector State
0
0
0
Unprotected—PPB and DYB are
changeable
0
0
1
Unprotected—PPB not
changeable, DYB is changeable
0
1
0
Protected—PPB and DYB are
changeable
1
0
0
1
1
0
0
1
1
Protected—PPB not
changeable, DYB is changeable
1
0
1
1
1
1
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