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™
Nonvolatile Elements while power is unavailable.
The nonvolatility of the STK16C68 does not require
any system intervention or support:
AutoStore-
Plus™
on power-down and automatic RECALL on
power-up guarantee data integrity without the use of
batteries.
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 (V
CC
< V
SWITCH
) at which point the part
depends only on its internal capacitor for
STORE
completion. This safe transfer of data from
SRAM
to
Nonvolatile Elements 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.
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 V
CC
and V
SS
, 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.
POWER-UP
RECALL
During power up, or after any low-power condition
(V
CC
< V
RESET
), an internal
RECALL
request will be
latched. When V
CC
once again exceeds the sense
voltage of V
SWITCH
, a
RECALL
cycle will automatically
be initiated and will take t
RESTORE
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 V
CC
or
between E and system V
CC
.
SRAM READ
The STK16C68 performs a
READ
cycle whenever E
and G are low and W is high. The address specified
on pins A
0-12
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 t
AVQV
(
READ
cycle #1). If the
READ
is
initiated by E or G, the outputs will be valid at t
ELQV
or
at t
GLQV
, whichever is later (
READ
cycle #2). The data
outputs will repeatedly respond to address changes
within the t
AVQV
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.
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
READ
s 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:
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 DQ
0-7
will be writ-
ten into the memory if it is valid t
DVWH
before the end
of a W controlled
WRITE
or t
DVEH
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 t
WLQZ
after W goes low.
March 2006
7
Document Control # ML0010 rev 0.2
SIMTEK [ SIMTEK CORPORATION ]
