STK14C88
Figure 1 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.
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, both VCC and VCAP are con-
nected to the + 5V power supply without the 68μF
capacitor. In this mode the AutoStore function of the
STK14C88 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. Read address
2. Read address
3. Read address
4. Read address
5. Read address
6. Read address
0E38 (hex)
31C7 (hex)
03E0 (hex)
3C1F (hex)
303F (hex)
0C63 (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 VCC can be tied to ground and + 5V applied to
VCAP (Figure 2). This is the AutoStore Inhibit mode,
in which the AutoStore function is disabled. If the
STK14C88 is operated in this configuration, refer-
ences to VCC should be changed to VCAP throughout
this data sheet. In this mode, STORE operations may
be triggered through software control or the HSB
pin. To enable or disable AutoStore using an IO port
pin, see “PREVENTING STORES” on page 12.
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.
AutoStore MODE
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-
initiated STORE cycles are performed regardless of
whether a WRITE operation has taken place.
The STK14C88 can be powered in one of three
modes.
During normal AutoStore operation, the STK14C88
will draw current from VCC to charge a capacitor con-
nected 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 VCC and initiate a
STORE operation.
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
Vcc and Vcap.
10kΩ∗
1
32
31
30
+
16
17
Figure 1: AutoStore Mode
Rev 2.0
Document Control #ML0014
Feb, 2008
10