STK14CA8
DEVICE OPERATION
nvSRAM
SRAM WRITE
The STK14CA8 nvSRAM is made up of two
functional components paired in the same physical
cell. These are a SRAM memory cell and a
nonvolatile QuantumTrap™ cell. The SRAM memory
cell operates as a standard fast static RAM. Data in
the SRAM can be transferred to the nonvolatile cell
(the STORE operation), or from the nonvolatile cell
to SRAM (the RECALL operation). This unique
architecture allows all cells to be stored and recalled
in parallel. During the STORE and RECALL
operations SRAM READ and WRITE operations are
inhibited. The STK14CA8 supports unlimited reads
and writes just like a typical SRAM. In addition, it
provides unlimited RECALL operations from the
nonvolatile cells and up to 1 million STORE
operations.
A WRITE cycle is performed whenever
E
and W
are low and HSB is high. 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 written 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
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 STK14CA8 stores data to nvSRAM using one of
three storage operations. These three operations are
Hardware Store, activated by HSB , Software Store,
actived by an address sequence, and AutoStore™, on
device power down.
SRAM READ
The STK14CA8 performs a READ cycle whenever
E
and
G
are low while
W
and HSB are high.
The address specified on pins A16-0 determines which
of the 131,072 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 transitions on
any control input pins, and will remain valid until
another address change or until E or G is brought
high, or W or HSB is brought low.
AutoStore™ operation is a unique feature of Simtek
QuantumTrap™ technology and is enabled by default
on the STK14CA8.
During normal operation, the device will draw current
from Vcc to charge a capacitor connected to the Vcap
pin. This stored charge will be used by the chip to
perform a single STORE operation. If the voltage on
the Vcc pin drops below Vswitch, the part will
automatically disconnect the Vcap pin from Vcc.
A
STORE operation will be initiated with power provided
by the Vcap capacitor.
VCC
Figure 4 shows the proper connection of the storage
capacitor (Vcap) for automatic store operation. Refer
to the DC CHARACTERISTICS table for the size of
Vcap. The voltage on the Vcap pin is driven to 5V by a
charge pump internal to the chip. A pull up should be
placed on W to hold it inactive during power up.
VCAP
VCC
W
To reduce unneeded nonvolatile stores, AutoStore™
and Hardware Store operations 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 a WRITE operation has taken place. The
HSB signal can be monitored by the system to detect
an AutoStore™ cycle is in progress.
Figure 4: AutoStoreTM Mode
December 2004
11
Document Control #ML0022 rev 1.0
SIMTEK [ SIMTEK CORPORATION ]
