參數(shù)資料
型號： W78M64V100SBC
廠商： WHITE ELECTRONIC DESIGNS CORP
元件分類： PROM
英文描述： 8M X 64 FLASH 3.3V PROM MODULE, 100 ns, PBGA159
封裝： 13 X 22 MM, 1.27 MM PITCH, PLASTIC, BGA-159
文件頁數(shù)： 9/54頁
文件大小： 1348K
代理商： W78M64V100SBC
17
White Electronic Designs Corporation (602) 437-1520 www.whiteedc.com
White Electronic Designs
W78M64V-XSBX
July 2006
Rev. 4
White Electronic Designs Corp. reserves the right to change products or specications without notice.
command sequences, the DYBs will be set or cleared, thus
placing each sector in the protected or unprotected state.
These are the 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
unprotected 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 difcult to change,
level of protection. The PPBs retain their state across power
cycles because they are non-volatile. Individual 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 protection.
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 operation.
The WP#/ACC write protect pin adds a final level of
hardware protection to sectors 0, 1, 268, and 269. When
this pin is low it is not possible 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 setting
up sector protection during system initialization.
It is possible to have sectors that have been persistently
locked, and sectors that are left in the dynamic state. The
sectors in the dynamic state are all unprotected. 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 unprotected, 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 reect
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 protect the boot
code by holding WP#/ACC = VIL.
TABLE 8. SECTOR PROTECTION SCHEMES
DYB
PPB
LOCK
SECTOR STATE
0
Unprotected - PPB and DYB are
changeable
0
1
Unprotected - PPB not changeable,
DYB is changeable
0
1
0
Protected - PPB and DYB are
changeable
100
110
0
1
Protected - PPB not changeable,
DYB is changeable
101
111
Table 8 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 dynamically 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 beforethe device returns to
read mode without having modied 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 sector.
The programming of the DYB, PPB, and PPB lock for a
given sect or can be ver i f ied 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 Sector
Protection mode locking bit exists to guarantee that the
device remain in software sector protection. Once set,
the Persistent Sector Protection locking bit prevents
programming of the password protection mode locking bit.
This guarantees that a hacker could not place the device
in password protection mode.
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