STK12C68 Simtek, STK12C68 Datasheet - Page 10

• Manufacturer Part Number: STK12C68
• Description: 8Kx8 AutoStore nvSRAM
• Manufacturer: Simtek

STK12C68 (SMD5962-94599)
Document Control #ML0008 Rev 0.7
SOFTWARE NONVOLATILE RECALL
A software
of
ware
the following sequence of
tions must be performed:
Internally,
SRAM
information is transferred into the
the t
ready for
operation in no way alters the data in the Nonvolatile
Elements. The nonvolatile data can be recalled an
unlimited number of times.
AutoStore OPERATION
The STK12C68 can be powered in one of three
modes.
During normal AutoStore operation, the STK12C68
will draw current from V
connected to the V
used by the chip to perform a single
tion. After power up, when the voltage on the V
pin drops below V
disconnect the V
STORE
Figure 2 shows the proper connection of capacitors
for automatic store operation. A charge storage
1. Read address
2. Read address
3. Read address
4. Read address
5. Read address
6. Read address
Figure 2. AutoStore Mode
READ
RECALL
February 2007
STORE
data is cleared, and second, the nonvolatile
operation.
operations in a manner similar to the soft-
READ
RECALL
+
cycle time the
RECALL
initiation. To initiate the
and
CAP
is a two-step procedure. First, the
CAP
SWITCH
cycle is initiated with a sequence
14
0000 (hex)
1555 (hex)
0AAA (hex)
1FFF (hex)
10F0 (hex)
0F0E (hex)
1
WRITE
pin from V
pin. This stored charge will be
, the part will automatically
CCX
15
27
SRAM
28
26
E
operations. The
controlled
to charge a capacitor
will once again be
Valid READ
Valid READ
Valid READ
Valid READ
Valid READ
Initiate RECALL cycle
CCX
SRAM
RECALL
Figure 3. System Power Mode
STORE
and initiate a
READ
cells. After
RECALL
opera-
opera-
cycle,
CAP
10
14
1
capacitor having a capacity of between 68μF and
220μF (± 20%) rated at 6V should be provided.
In system power mode (Figure 3), both V
are connected to the + 5V power supply without the
68μF capacitor. In this mode the AutoStore function
of the STK12C68 will operate on the stored system
charge as power goes down. The user must, how-
ever, guarantee that V
during the 10ms
If an automatic
then V
V
which the AutoStore function is disabled. If the
STK12C68 is operated in this configuration, refer-
ences to V
this data sheet. In this mode,
be triggered through software control or the HSB pin.
It is not permissible to change between these three
options “on the fly.”
In order to prevent unneeded
automatic
externally driving HSB low will be ignored unless at
least one
most recent
ated
whether a
optional pull-up resistor is shown connected to HSB.
This can be used to signal the system that the
AutoStore cycle is in progress.
If the power supply drops faster than 20 μs/volt
before V
should be inserted between V
supply to avoid momentary excess of current
between Vccx and Vcap.
CAP
26
28
27
15
(Figure 4). This is the AutoStore Inhibit mode, in
STORE
CCX
CCX
WRITE
can be tied to ground and + 5V applied to
CCX
STORE
WRITE
reaches V
STORE
should be changed to V
cycles are performed regardless of
STORE
Figure 4. AutoStore Inhibit Mode
STORE
operation has taken place since the
s as well as those initiated by
operation has taken place. An
or
SWITCH
CCX
on power loss is not required,
RECALL
cycle.
does not drop below 3.6V
, then a 2.2 ohm resistor
STORE
14
1
cycle. Software initi-
CCX
STORE
and the system
operations may
28
27
26
15
CAP
CCX
operations,
throughout
and V
CAP