Applying the STK11C/15C/16C88
line should preferably be held high during the entire
Write cycle to avoid bus contention on the data
lines.
the system to stabilize before attempting nvSRAM
accesses.
Data can also be recalled under software control in
a manner similar to the STORE operation. Six
addresses are read in sequence to initiate the trans-
fer from nonvolatile memory to SRAM. The following
address sequence is used to start a memory
RECALL:
The STK11C88, STK15C88 and STK16C88 are
high speed memories and therefore must have a
high frequency bypass capacitor of approximately
0.1µF connected between VCC and ground. As with
all high speed CMOS integrated circuits, careful
routing of power, ground and signals will help to
reduce noise induced problems.
1. Read Address 0E38H
2. Read Address 31C7H
3. Read Address 03E0H
4. Read Address 3C1FH
5. Read Address 303FH
6. Read Address 0C63H (Initiate Recall Cycle)
STK11C88 Nonvolatile Operations
nvSRAM Store
The STK11C88 is a member of Simtek's “Software
Store” nvSRAM family, and is designed for easy in-
circuit programmability. Data that has been written
to the STK11C88's SRAM is Stored to nonvolatile
memory by reading six specific SRAM addresses in
sequence. The Store operation is completely auton-
omous from that point, and requires no processor
support nor external glue logic to complete. Once
the STORE process is initiated, the STK11C88 is
disabled and no SRAM accesses are allowed until
the Store operation is completed (<10 ms). It is
important that Read operations be used instead of
Writes. SRAM Writes will invalidate the sequence.
The following address sequence is used to start a
memory STORE operation:
It takes a maximum of 20µs for data that was Stored
in nonvolatile memory to be Recalled to SRAM.
STK15C88 Nonvolatile Operations
The STK15C88 is very similar in operation to the
STK11C88. Its software STORE and RECALL oper-
ations, and its power-up RECALL capabilities are
identical. The STK15C88 adds the capability of
Simtek's AutoStore™ technology that allows it to
sense power loss and STORE data to nonvolatile
memory autonomously without external circuitry or
processor intervention. As with the STK11C88, once
data is stored into nonvolatile memory, no batteries,
capacitors or external power sources are required to
safely maintain the data for a minimum of 10 years.
The only requirement for full AutoStore™ operation
is that power supply voltage remain above 3.6 volts
for a minimum of 10ms after VSWITCH (approxi-
mately 4.25 volts, see Figure 2).
1. Read Address 0E38H
2. Read Address 31C7H
3. Read Address 03E0H
4. Read Address 3C1FH
5. Read Address 303FH
6. Read Address 0FC0H (Initiate STORE Cycle)
5
The chance of inadvertently reading the correct six
addresses in sequence, and accidentally corrupting
the data Stored in the STK11C88's nonvolatile sec-
tion, is less than 1 chance in 1025.
Vcc
4
AutoStoreTM Cycle in Progress
3
2
nvSRAM Recall
Store
Time
1
STK11C88 data is Recalled from nonvolatile mem-
ory to SRAM during power-up. A RECALL is auto-
matically initiated when internal circuitry senses
VCC levels rising above approximately 4.25 volts
15
30
45
60
75
90
105
135
120
Time (ms)
(VSWITCH).
Embedded
processor
wake-up
Figure 2:
sequences (power-on reset), should be delayed for
a minimum of 550µs (tRESTORE) after VSWITCH to
assure that data is completely recalled and to allow
STK15C88 AutoStore™ Vcc Requirements
Even if the design engineer cannot guarantee the
10ms power supply voltage requirement, it is still
possible to use the STK15C88 in many applications.
8-22
SIMTEK [ SIMTEK CORPORATION ]
