STK16CA8
DEVICE OPERATION
The STK16CA8 has two separate modes of opera-
tion:
SRAM
mode and nonvolatile mode. In
SRAM
mode, the memory operates as a standard fast
static
RAM
. In nonvolatile mode, data is transferred
from
SRAM
to the nonvolatile elements (the
STORE
operation) or from the nonvolatile elements to
SRAM
(the
RECALL
operation). In this mode
SRAM
func-
tions are disabled.
one
WRITE
operation has taken place since the most
recent
STORE
or
RECALL
cycle. Software initiated
STORE
cycles are performed regardless of whether
or not a
WRITE
operation has taken place.
POWER-UP
RECALL
During power up, or after any low-power condition
(V
CCX
< V
SWITCH
), an internal
RECALL
request will be
latched. When V
CC
once again exceeds the sense
voltage of V
SWITCH
, a
RECALL
cycle will automatically
be initiated and will take t
RESTORE
to complete.
If the STK16CA8 is in a
WRITE
state at the end of
power-up
RECALL
, the
WRITE
will be inhibited and E
or W must be brought high and then low for a write
to initiate.
SRAM READ
The STK16CA8 performs a
READ
cycle whenever E
and G are low and W is high. The address specified
on pins A
0-16
determines which of the 131,072 data
bytes will be accessed. When the
READ
is initiated
by an address transition, the outputs will be valid
after a delay of t
AVQV
(
READ
cycle #1). If the
READ
is
initiated by E or G, the outputs will be valid at t
ELQV
or
at t
GLQV
, whichever is later (
READ
cycle #2). The data
outputs will repeatedly respond to address changes
within the t
AVQV
access time without the need for tran-
sitions on any control input pins, and will remain valid
until new output data appears or until E or G is
brought high, or W is brought low.
SOFTWARE NONVOLATILE
STORE
The STK16CA8 software
STORE
cycle is initiated by
executing sequential
E
controlled
READ
cycles from
six specific address locations. During the
STORE
cycle an erase of the previous nonvolatile data is
first performed, followed by a program of the nonvol-
atile elements. The program operation copies the
SRAM
data into nonvolatile memory. Once a
STORE
cycle is initiated, further input and output are dis-
abled until the cycle is completed.
Because a sequence of
READ
s from specific
addresses is used for
STORE
initiation, it is impor-
tant that no other
READ
or
WRITE
accesses inter-
vene in the sequence, or the sequence will be
aborted and no
STORE
or
RECALL
will take place.
To initiate the software
STORE
cycle, the following
READ
sequence must be performed:
1.
2.
3.
4.
5.
6.
Read address
Read address
Read address
Read address
Read address
Read address
4E38 (hex)
B1C7 (hex)
83E0 (hex)
7C1F (hex)
703F (hex)
8FC0 (hex)
Valid READ
Valid READ
Valid READ
Valid READ
Valid READ
Initiate
STORE
cycle
SRAM WRITE
A
WRITE
cycle is performed whenever E and W are
low. The address inputs must be stable prior to
entering the
WRITE
cycle and must remain stable
until either E or W goes high at the end of the cycle.
The data on the common I/O pins DQ
0-7
will be writ-
ten into the memory if it is valid t
DVWH
before the end
of a W controlled
WRITE
or t
DVEH
before the end of an
E controlled
WRITE
.
It is recommended that G be kept high during the
entire
WRITE
cycle to avoid data bus contention on
the common I/O lines. If G is left low, internal circuitry
will turn off the output buffers t
WLQZ
after W goes low.
AutoStorePlus™
OPERATION
The STK16CA8’s automatic
STORE
on power-down
is completely transparent to the system. The
AutoStore™
initiation takes less than 500ns when
power is lost (V
CC
< V
SWITCH
) at which point the part
depends only on its internal capacitor for
STORE
completion.
In order to prevent unneeded
STORE
operations,
automatic
STORE
s will be ignored unless at least
The software sequence must be clocked with E con-
trolled
READ
s.
Once the sixth address in the sequence has been
entered, the
STORE
cycle will commence and the
chip will be disabled. It is important that
READ
cycles
and not
WRITE
cycles be used in the sequence, and
it is necessary that G be low for the sequence to be
September 2003
8
Document Control # ML0023 rev 0.1
SIMTEK [ SIMTEK CORPORATION ]
