X28HT010
DEVICE OPERATION
Read
Read operations are initiated by both
OE
and
CE
LOW.
The read operation is terminated by either
CE
or
OE
returning HIGH. This two line control architecture elimi-
nates bus contention in a system environment. The data
bus will be in a high impedance state when either
OE
or
CE
is HIGH.
Write
Write operations are initiated when both
CE
and
WE
are
LOW and
OE
is HIGH. The X28HT010 supports both a
CE
and
WE
controlled write cycle. That is, the address
is latched by the falling edge of either
CE
or
WE,
whichever occurs last. Similarly, the data is latched
internally by the rising edge of either
CE
or
WE,
which-
ever occurs first. A byte write operation, once initiated,
will automatically continue to completion, typically within
5ms.
Page Write Operation
The page write feature of the X28HT010 allows the
entire memory to be written in 5 seconds. Page write
allows two to two hundred fifty-six bytes of data to be
consecutively written to the X28HT010 prior to the
commencement of the internal programming cycle. The
host can fetch data from another device within the
system during a page write operation (change the source
address), but the page address (A
8
through A
16
) for
each subsequent valid write cycle to the part during this
operation must be the same as the initial page address.
The page write mode can be initiated during any write
operation. Following the initial byte write cycle, the host
can write an additional one to two hundred fifty-six bytes
in the same manner as the first byte was written. Each
successive byte load cycle, started by the
WE
HIGH to
LOW transition, must begin within 100µs of the falling
edge of the preceding
WE.
If a subsequent
WE
HIGH to
LOW transition is not detected within 100µs, the internal
automatic programming cycle will commence. There is
no page write window limitation. Effectively the page
write window is infinitely wide, so long as the host
continues to access the device within the byte load cycle
time of 100µs.
HARDWARE DATA PROTECTION
The X28HT010 provides three hardware features that
protect nonvolatile data from inadvertent writes.
•
•
Default V
CC
Sense—All functions are inhibited when
V
CC
is
≤3.4V.
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.
SYSTEM CONSIDERATIONS
Because the X28HT010 is frequently used in large
memory arrays it is provided with a two line control
architecture for both read and write operations. Proper
usage can provide the lowest possible power dissipation
and eliminate the possibility of contention where mul-
tiple I/O pins share the same bus.
It has been demonstrated that markedly higher tem-
perature performance can be obtained from this device
if
CE
is left enabled throughout the read and write
operation.
To gain the most benefit it is recommended that
CE
be
decoded from the address bus and be used as the
primary device selection input. Both
OE
and
WE
would
then be common among all devices in the array. For a
read operation this assures that all deselected devices
are in their standby mode and that only the selected
device(s) is outputting data on the bus.
Because the X28HT010 has two power modes, standby
and active, proper decoupling of the memory array is of
prime concern. Enabling
CE
will cause transient current
spikes. The magnitude of these spikes is dependent on
the output capacitive loading of the I/Os. Therefore, the
larger the array sharing a common bus, the larger the
transient spikes. The voltage peaks associated with the
current transients can be suppressed by the proper
selection and placement of decoupling capacitors. As a
minimum, it is recommended that a 0.1µF high fre-
quency ceramic capacitor be used between V
CC
and
V
SS
at each device. Depending on the size of the array,
the value of the capacitor may have to be larger.
In addition, it is recommended that a 4.7µF electrolytic
bulk capacitor be placed between V
CC
and V
SS
for each
eight devices employed in the array. This bulk capacitor
is employed to overcome the voltage droop caused by
the inductive effects of the PC board traces.
•
Noise Protection—A
WE
pulse less than 10ns will not
initiate a write cycle.
3
XICOR [ XICOR INC. ]
