Applying the STK11C/15C/16C88
reset condition for a minimum of 550µs after VCC
reaches VSWITCH (about 4.25V). This allows suffi-
cient time for the STK11C88 to Recall data from its
nonvolatile memory into SRAM. After system reset
is released the EPF81500 will request data from the
STK11C88 (pull CONF_DONE line low) and begin
sending addresses in a sequential count up or count
down manner. After data is loaded into the EPLD, it
will release the CONF_DONE line allowing the
STK11C88 to be accessed by the embedded micro-
processor. It is required that the microprocessor be
held in reset until the EPF81500 is finished loading.
This simple approach solves the problem of needing
both fast SRAM scratch pad memory and nonvola-
tile memory to load the Altera device.
tile SRAMs efficiently replaces Battery Backed
RAM, and results in higher reliability and higher per-
formance products. The “C88” nvSRAM family also
replaces the combination of SRAM and EEPROM
presently used in many stand-alone applications to
get around Battery Backed RAM's inherent limita-
tions. The resulting savings in board space, power,
and cost makes the nvSRAM an attractive design
option.
RD
WE
16 Bit Data Bus
W
W
G
G
Texas
Instruments
Simtek
STK15C88
AutoStoreTM
Data
Simtek
STK11C88
nvSRAM and TI-TMS320C52
TMS320C52
(DSP)
Program
Memory
Use of Simtek’s 256K parts allows the TMS320C52
to run at its fully rated 80 megahertz with no wait-
states. This design approach also assures that all
calculated or measured control variables are saved
in the event of power failure. No glue logic or inter-
face components are required for systems of up to
96K words of nonvolatile memory, and only minimal
external logic for systems of up to 192K words. This
compact, efficient memory design simplifies PCB
layout, improves system reliability, and reduces
cost. Since memory data is safe when power fails,
short VCC drop-outs will not necessarily result in
loss of control or require system re-boot. If the on-
board real-time clock maintains nonvolatile elapsed
time knowledge, recovery may be possible without
loss of control or unstable operation.
Memory
E
E
Address Bus (A0-A14)
DS
PS
DECODER
IS
A15
Figure 5
High Performance Embedded DSP System Using
the TMS320C52 with the Simtek STK11C/15C88
Simtek's nvSRAMs also have many advantages
over fast FLASH memory, including a single byte
write, single operating voltage (5V), faster access
times, and unlimited SRAM Write cycles. nvSRAMs
also have the ability to perform Store operations
autonomously without processor intervention or the
requirement to run FLASH store algorithms. This
results in less processor overhead, reduced parts
count and higher product reliability.
Use of the STK11C88 for program memory guaran-
tees that control code will not be lost during power
dropouts, but still allows code changes to be made
in-circuit without special equipment or hardware
modifications. This is of special value in applications
such as security systems where periodic updates to
password files or access lists are required, but
where nonvolatility is a necessity (Figure 5).
The Simtek “C88” family of nonvolatile memories is
fast, versatile, and cost effective for many types of
modern high performance designs. The combination
of speed and nonvolatility in one package allows
high technology processing engines to operate at
their full potential. The added advantage of remote
programmability without the need to modify hard-
ware, simplifies field upgrades and lengthens prod-
uct lifetimes.
Conclusion
Applications for Battery Backed RAM are limited by
the temperature range over which batteries operate
reliably. Lithium batteries have shortened life spans
at high temperature and electro-chemical inefficien-
cies at low temperature. Battery Backed RAMs are
also slower than nvSRAMs, and therefore are not
suited to many high performance embedded proces-
sor applications. Use of Simtek’s family of nonvola-
8-24
SIMTEK [ SIMTEK CORPORATION ]
