STK16C68-S20 데이터 시트보기 (PDF) - Simtek Corporation
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STK16C68-S20 Datasheet PDF : 9 Pages
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STK16C68
DEVICE OPERATION
The AutoStorePlus™ STK16C68 is a fast 8K x 8
SRAM that does not lose its data on power-down.
The data is preserved in integral QuantumTrap™
EEPROM while power is unavailable. The nonvolatil-
ity of the STK16C68 does not require any system
intervention or support: AutoStorePlus™ on power-
down and automatic RECALL on power-up guaran-
tee data integrity without the use of batteries.
NOISE CONSIDERATIONS
Note that the STK16C68 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 STK16C68 performs a READ cycle whenever E
and G are low and W is high. The address specified
on pins A0-12 determines which of the 8,192 data
bytes will be accessed. When the READ is initiated
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 tran-
sitions on any control input pins, and will remain valid
until another address change or until E or G is
brought high or W is brought low.
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.
AutoStorePlus™ OPERATION
The STK16C68’s automatic STORE on power-down
is completely transparent to the system. The
AutoStore™ 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. This safe transfer of data from SRAM to
EEPROM takes place regardless of power supply
slew rate.
In order to prevent unneeded STORE operations, the
automatic STORE 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 STK16C68 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 STK16C68 software STORE cycle is initiated by
executing sequential READ cycles from six specific
address locations. During the STORE cycle an erase
of the previous nonvolatile data is first performed,
followed by a program of the nonvolatile elements.
The program operation copies the SRAM data into
nonvolatile memory. Once a STORE cycle is initi-
ated, 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:
July 1999
4-79
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