STK12C68 (SMD5962-94599)
capacitor having a capacity of between 68μF and
220μF ( 20%) rated at 6V should be provided.
SOFTWARE NONVOLATILE RECALL
A software RECALL cycle is initiated with a sequence
of READ operations in a manner similar to the soft-
ware STORE initiation. To initiate the RECALL cycle,
the following sequence of E controlled READ opera-
tions must be performed:
In system power mode (Figure 3), both VCCX and VCAP
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 VCCX does not drop below 3.6V
during the 10ms STORE cycle.
1. Read address
2. Read address
3. Read address
4. Read address
5. Read address
6. Read address
0000 (hex)
1555 (hex)
0AAA (hex)
1FFF (hex)
10F0 (hex)
0F0E (hex)
Valid READ
Valid READ
Valid READ
Valid READ
Valid READ
Initiate RECALL cycle
If an automatic STORE on power loss is not required,
then VCCX can be tied to ground and + 5V applied to
VCAP (Figure 4). This is the AutoStore Inhibit mode, in
which the AutoStore function is disabled. If the
STK12C68 is operated in this configuration, refer-
ences to VCCX should be changed to VCAP throughout
this data sheet. In this mode, STORE operations may
be triggered through software control or the HSB pin.
It is not permissible to change between these three
options “on the fly.”
Internally, RECALL is a two-step procedure. First, the
SRAM data is cleared, and second, the nonvolatile
information is transferred into the SRAM cells. After
the tRECALL cycle time the SRAM will once again be
ready for READ and WRITE operations. The RECALL
operation in no way alters the data in the Nonvolatile
Elements. The nonvolatile data can be recalled an
unlimited number of times.
In order to prevent unneeded STORE operations,
automatic STOREs as well as those initiated by
externally driving HSB low will be ignored unless at
least one WRITE operation has taken place since the
most recent STORE or RECALL cycle. Software initi-
ated STORE cycles are performed regardless of
whether a WRITE operation has taken place. An
optional pull-up resistor is shown connected to HSB.
This can be used to signal the system that the
AutoStore cycle is in progress.
AutoStore OPERATION
The STK12C68 can be powered in one of three
modes.
During normal AutoStore operation, the STK12C68
will draw current from VCCX to charge a capacitor
connected to the VCAP pin. This stored charge will be
used by the chip to perform a single STORE opera-
tion. After power up, when the voltage on the VCAP
pin drops below VSWITCH, the part will automatically
disconnect the VCAP pin from VCCX and initiate a
STORE operation.
If the power supply drops faster than 20 μs/volt
before VCCX reaches VSWITCH, then a 2.2 ohm resistor
should be inserted between VCCX and the system
supply to avoid momentary excess of current
between Vccx and Vcap.
Figure 2 shows the proper connection of capacitors
for automatic store operation. A charge storage
28
27
26
1
1
28
27
26
1
28
27
26
+
14
15
14
15
14
15
Figure 4. AutoStore Inhibit Mode
Figure 3. System Power Mode
Figure 2. AutoStore Mode
Rev 0.7
Document Control #ML0008
February 2007
10
SIMTEK [ SIMTEK CORPORATION ]
