STK14C88-NF35UTR Просмотр технического описания (PDF) - Simtek Corporation
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STK14C88-NF35UTR Datasheet PDF : 15 Pages
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STK14C88-NF35U
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. 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
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
The STK14C88-NF35U can be powered in one of
three modes.
During normal AutoStore operation, the STK14C88-
NF35U will draw current from VCC to charge a capac-
itor 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 automati-
cally disconnect the VCAP pin from VCC and initiate a
STORE operation.
Figure 2 shows the proper connection of capacitors
for automatic store operation. A charge storage
10kΩ∗
1
32
31
30
capacitor having a capacity of between 68μF and
220μF (± 20%) rated at 6V should be provided.
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-NF35U will operate on the stored sys-
tem charge as power goes down. The user must,
however, guarantee that VCC does not drop below
3.6V during the 10ms STORE 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-
initiated STORE cycles are performed regardless of
whether a WRITE operation has taken place.
If the power supply drops faster than 20 μs/volt
before VCC reaches VSWITCH, then a 2.2 ohm resistor
should be inserted between the VCC pin on the IC
and the system supply to avoid momentary excess
of current between Vcc and Vcap.
AutoStore INHIBIT MODE
If an automatic STORE on power loss is not
required, then Vcc can be tied to ground and system
power applied to VCAP (Figure 3). This is the
AutoStore Inhibit mode, in which the AutoStore func-
tion is disabled. If the STK14C88-NF35U is oper-
ated in this configuration, references to Vcc should
be changed to VCAP throughout this data sheet. In
this mode, STORE operations may be triggered
through software control. It is not permissible to
change between these three options “on the fly.”
1
32
31
30
+
16
17
Figure 2: AutoStore Mode
*If HSB is not used, it should be left unconnected.
Document Control #ML0066 Rev 2.0
10
Feb, 2008
16
17
Figure 3: AutoStore Inhibit Mode
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