STK11C68
Internally,
RECALL
is a two-step procedure. First,
the
SRAM
data is cleared, and second, the nonvola-
tile 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.
HARDWARE PROTECT
The STK11C68 offers hardware protection against
inadvertent
STORE
operation during low-voltage
conditions. When V
CC
< V
SWITCH
, software
STORE
operations are inhibited.
LOW AVERAGE ACTIVE POWER
The STK11C68 draws significantly less current
when it is cycled at times longer than 50ns. Figure 2
shows the relationship between I
CC
and
READ
cycle
time. Worst-case current consumption is shown for
both
CMOS
and
TTL
input levels (commercial tem-
perature range, V
CC
= 5.5V, 100% duty cycle on chip
enable). Figure 3 shows the same relationship for
WRITE
cycles. If the chip enable duty cycle is less
than 100%, only standby current is drawn when the
chip is disabled. The overall average current drawn
by the STK11C68 depends on the following items:
1)
CMOS
vs.
TTL
input levels; 2) the duty cycle of
chip enable; 3) the overall cycle rate for accesses;
4) the ratio of
READ
s to
WRITE
s; 5) the operating
temperature; 6) the V
cc
level; and 7) I/O loading.
100
POWER-UP
RECALL
During power up, or after any low-power condition
(V
CC
< V
RESET
), 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 STK11C68 is in a
WRITE
state at the end of
power-up
RECALL
, the
SRAM
data will be corrupted.
To help avoid this situation, a 10K Ohm resistor
should be connected either between W and system
V
CC
or between E and system V
CC
.
100
Average Active Current (mA)
Average Active Current (mA)
80
80
60
60
TTL
CMOS
20
40
TTL
20
CMOS
0
50
100
150
Cycle Time (ns)
200
40
0
50
100
150
Cycle Time (ns)
200
Figure 2: I
CC
(max) Reads
Figure 3: I
CC
(max) Writes
March 2006
8
Document Control # ML0007 rev 0.2
CYPRESS [ CYPRESS SEMICONDUCTOR ]
