STK16C88-3WF35I Ver la hoja de datos (PDF) - Simtek Corporation
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STK16C88-3WF35I Datasheet PDF : 13 Pages
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STK16C88-3
nvSRAM OPERATION
The AutoStore+ STK16C88-3 is a fast 32K x 8
SRAM that does not lose its data on power-down.
The data is preserved in integral Quantum Trap non-
volatile storage elements when power is lost. Auto-
matic STORE on power-down and automatic
RECALL on power-up guarantee data integrity with-
out the use of batteries.
NOISE CONSIDERATIONS
Note that the STK16C88-3 is a high-speed memory
and so must have a high-frequency bypass capaci-
tor of approximately 0.1μF connected between VCC
and VSS, using leads and traces that are as short as
possible. As with all high-speed CMOS ICs, normal
careful routing of power, ground and signals will help
prevent noise problems.
SRAM READ
The STK16C88-3 performs a READ cycle whenever
E and G are low and W is high. The address speci-
fied on pins A0-14 determines which of the 32,768
data bytes will be accessed. When the READ is initi-
ated by an address transition, the outputs will be
valid after a delay of tAVQV (READ cycle #1). If the
READ is initiated by E or G, the outputs will be valid
at tELQV or at tGLQV, whichever is later (READ cycle #2).
The data outputs will repeatedly respond to address
changes within the tAVQV access time without the need
for transitions on any control input pins, and will
remain valid until another address change or until E
or G is brought high.
SRAM WRITE
A WRITE cycle is performed whenever E and W are
low. The address inputs must be stable prior to
entering the WRITE cycle and must remain stable
until either E or W goes high at the end of the cycle.
The data on the common I/O pins DQ0-7 will be writ-
ten into the memory if it is valid tDVWH before the end
of a W controlled WRITE or tDVEH before the end of an
E controlled WRITE.
It is recommended that G be kept high during the
entire WRITE cycle to avoid data bus contention on
the common I/O lines. If G is left low, internal circuitry
will turn off the output buffers tWLQZ after W goes low.
AutoStore+ OPERATION
The STK16C88-3’s automatic STORE on power-
down is completely transparent to the system. The
STORE initiation takes less than 500ns when power
is lost (VCC < VSWITCH) at which point the part depends
only on its internal capacitor for STORE completion.
If the power supply drops faster than 20μs/volt
before Vcc reaches Vswitch, then a 1 ohm resistor
should be inserted between Vcc and the system
supply to avoid a momentary excess of current
between Vcc and internal capacitor.
In order to prevent unneeded STORE operations,
automatic STOREs will be ignored unless at least
one WRITE operation has taken place since the most
recent STORE or RECALL cycle. Software initiated
STORE cycles are performed regardless of whether
or not a WRITE operation has taken place.
POWER-UP RECALL
During power up, or after any low-power condition
(VCC < VRESET), an internal RECALL request will be
latched. When VCC once again exceeds the sense
voltage of VSWITCH, a RECALL cycle will automatically
be initiated and will take tRESTORE to complete.
If the STK16C88-3 is in a WRITE state at the end of
power-up RECALL, the SRAM data will be corrupted.
To help avoid this situation, a 10kΩ resistor should
be connected either between W and system VCC or
between E and system VCC.
SOFTWARE NONVOLATILE STORE
The STK16C88-3 software STORE cycle is initiated
by executing sequential READ cycles from six spe-
cific address locations. During the STORE cycle, pre-
vious nonvolatile data is erased and then the SRAM
contents are written to the nonvolatile storage ele-
ments. Once a STORE cycle is initiated, further input
and output are disabled until the cycle is completed.
Because a sequence of READs from specific
addresses is used for STORE initiation, it is impor-
tant that no other READ or WRITE accesses inter-
vene in the sequence or the sequence will be
aborted and no STORE or RECALL will take place.
To initiate the software STORE cycle, the following
READ sequence must be performed:
Document Control #ML0019 Rev 2.0
8
Jan, 2008
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