STK12C68
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:
1.
2.
3.
4.
5.
6.
Read address
Read address
Read address
Read address
Read address
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
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.
In system power mode (Figure 3), both V
CCX
and
V
CAP
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,
however, guarantee that V
CCX
does not drop below
3.6V during the 10ms
STORE
cycle.
If an automatic
STORE
on power loss is not required,
then V
CCX
can be tied to ground and + 5V applied to
V
CAP
(Figure 4). This is the
AutoStore™
Inhibit
mode, in which the
AutoStore™
function is disabled.
If the STK12C68 is operated in this configuration,
references to V
CCX
should be changed to V
CAP
throughout this data sheet. In this mode,
STORE
operations may be triggered through software con-
trol or the HSB pin. It is not permissable to change
between these three options “on the fly”.
In order to prevent unneeded
STORE
operations,
automatic
STORE
s 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. 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 t
RECALL
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™
OPERATION
The STK12C68 can be powered in one of three
modes.
During normal
AutoStore™
operation, the
STK12C68 will draw current from V
CCX
to charge a
capacitor connected to the V
CAP
pin. This stored
charge will be used by the chip to perform a single
STORE
operation. After power up, when the voltage
on the V
CAP
pin drops below V
SWITCH
, the part will
automatically disconnect the V
CAP
pin from V
CCX
and
initiate a
STORE
operation.
10kΩ
0.1μF
Bypass
10kΩ
1
28
27
26
14
15
10kΩ
10kΩ∗
1
28
27
26
1
28
27
26
68μF
6v, ±20%
+
0.1μF
Bypass
0.1μF
Bypass
14
14
15
15
Figure 2:
AutoStore™
Mode
Figure 3: System Power Mode
Figure 4:
AutoStore™
Inhibit Mode
*If HSB is not used, it should be left unconnected.
March 2006
9
Document Control # ML0008 rev 0.5
10kΩ∗
10kΩ∗
CYPRESS [ CYPRESS SEMICONDUCTOR ]
