X28C010KM-25 Datasheet, PDF (6/20 Pages) Intersil Corporation – Protects data against system level inadvertent writes

X28C010, X28HT010
Last Write
Load Accum
From Addr N
Compare
Accum with
Addr N
Compare
No
Ok?
Yes
Ready
FIGURE 5. TOGGLE BIT SOFTWARE FLOW
The Toggle Bit can eliminate the software housekeeping
chore of saving and fetching the last address and data
written to a device in order to implement DATA Polling. This
can be especially helpful in an array comprised of multiple
X28C010/X28HT010 memories that is frequently updated.
Toggle Bit Polling can also provide a method for status
checking in multiprocessor applications. The timing diagram
in Figure 4 illustrates the sequence of events on the bus.
The software flow diagram in Figure 5 illustrates a method
for polling the Toggle Bit.
Hardware Data Protection
The X28C010/X28HT010 provides three hardware features
that protect nonvolatile data from inadvertent writes.
• Noise Protection—A WE pulse less than 10ns will not
initiate a write cycle.
• Default V_CC Sense—All functions are inhibited when V_CC
is ≤ 3.5V.
• Write inhibit—Holding either OE LOW, WE HIGH, or CE
HIGH will prevent an inadvertent write cycle during power-
up and power-down, maintaining data integrity.
Software Data Protection
The X28C010/X28HT010 offers a software controlled data
protection feature. The X28C010/X28HT010 is shipped from
Intersil with the software data protection NOT ENABLED:
that is the device will be in the standard operating mode. In
this mode data should be protected during power-up/-down
operations through the use of external circuits. The host
would then have open read and write access of the device
once V_CC was stable.
The X28C010/X28HT010 can be automatically protected
during power-up and power-down without the need for
external circuits by employing the software data protection
feature. The internal software data protection circuit is
enabled after the first write operation utilizing the software
algorithm. This circuit is nonvolatile and will remain set for
the life of the device unless the reset command is issued.
Once the software protection is enabled, the
X28C010/X28HT010 is also protected from inadvertent and
accidental writes in the powered-up state. That is, the
software algorithm must be issued prior to writing additional
data to the device.
Software Algorithm
Selecting the software data protection mode requires the
host system to precede data write operations by a series of
three write operations to three specific addresses. Refer to
Figures 6 and 7 for the sequence. The three byte sequence
opens the page write window enabling the host to write from
one to two hundred fifty-six bytes of data. Once the page
load cycle has been completed, the device will automatically
be returned to the data protected state.
6
FN8105.1
February 12, 2007