STK12C68, STK12C68-5 (SMD5962-94599)
VCAP (Figure 3). This is the AutoStore Inhibit mode, in
SOFTWARE NONVOLATILE RECALL
which the AutoStore function is disabled. If the
STK12C68, STK12C68-5 is operated in this configu-
ration, references to VCC should be changed to VCAP
throughout this data sheet. In this mode, STORE
operations may be triggered through software con-
trol or the HSB pin. To enable or disable AutoStore
using an IO port pin, see “PREVENTING STORES”
on page 11.
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:
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
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.
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.
If the power supply drops faster than 20 μs/volt
before VCC reaches VSWITCH, then a 2.2 ohm resistor
should be inserted between VCC and the system sup-
ply to avoid momentary excess of current between
AutoStore MODE
The STK12C68, STK12C68-5 can be powered in
one of three modes.
Vcc and Vcap
.
During normal AutoStore operation, the STK12C68,
STK12C68-5 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. After power up, when the voltage
on the VCAP pin drops below VSWITCH, the part will
automatically disconnect the VCAP pin from VCC and
initiate a STORE operation.
1
28
27
26
+
Figure 2 shows the proper connection of capacitors
for automatic store operation. A charge storage
capacitor having a capacity of between 68μF and
220μF (± 20%) rated at 6V should be provided.
14
15
Figure 2: AutoStore Mode
*If HSB is not used, it should be left unconnected.
In system power mode, both VCC and VCAP are con-
nected to the + 5V power supply without the 68μF
capacitor. In this mode the AutoStore function of the
STK12C68, STK12C68-5 will operate on the stored
system charge as power goes down. The user must,
however, guarantee that VCC does not drop below
3.6V during the 10ms STORE cycle.
1
28
27
26
AutoStore INHIBIT MODE
14
15
If an automatic STORE on power loss is not required,
then VCC can be tied to ground and + 5V applied to
Figure 3: AutoStore Inhibit Mode
Rev 2.0
Document Control #ML0008
June, 2008
10
SIMTEK [ SIMTEK CORPORATION ]
