STK12C68 Simtek, STK12C68 Datasheet - Page 11

• Manufacturer Part Number: STK12C68
• Description: 8Kx8 AutoStore nvSRAM
• Manufacturer: Simtek

Document Control #ML0008 Rev 0.7
HSB OPERATION
The STK12C68 provides the HSB pin for controlling
and acknowledging the
pin is used to request a hardware
When the HSB pin is driven low, the STK12C68 will
conditionally initiate a
an actual
the
RECALL
driver that is internally driven low to indicate a busy
condition while the
is in progress.
SRAM READ
progress when HSB is driven low by any means are
given time to complete before the
is initiated. After HSB goes low, the STK12C68 will
continue
multiple
WRITE
be allowed a time, t
SRAM WRITE
will be inhibited until HSB returns high.
The HSB pin can be used to synchronize multiple
STK12C68s while using a single larger capacitor. To
operate in this mode the HSB pin should be con-
nected together to the HSB pins from the other
STK12C68s. An external pull-up resistor to + 5V is
required since HSB acts as an open drain pull down.
The V
be tied together and share a single capacitor. The
capacitor size must be scaled by the number of
devices connected to it. When any one of the
STK12C68s detects a power loss and asserts HSB,
the common HSB pin will cause all parts to request
a
STK12C68s that have been written since the last
nonvolatile cycle).
During any
was initiated, the STK12C68 will continue to drive
the HSB pin low, releasing it only when the
complete. Upon completion of the
the STK12C68 will remain disabled until the HSB
pin returns high.
STORE
SRAM
February 2007
CAP
is in progress when HSB is pulled low it will
SRAM READ
cycle. The HSB pin acts as an open drain
SRAM
pins from the other STK12C68 parts can
STORE
cycle (a
took place since the last
STORE
cycles requested after HSB goes low
and
operations for t
cycle will only begin if a
STORE
STORE
WRITE
DELAY
operation, regardless of how it
operations may take place. If a
STORE
STORE
, to complete. However, any
(initiated by any means)
will take place in those
operations that are in
operation after t
operations. The HSB
DELAY
STORE
STORE
. During t
STORE
STORE
operation
operation
WRITE
STORE
cycle.
DELAY
DELAY
or
to
is
11
;
,
If HSB is not used, it should be left unconnected.
PREVENTING STORES
The
holding HSB high with a driver capable of sourcing
30mA at a V
overpower the internal pull-down device that drives
HSB low for 20μs at the onset of a
the STK12C68 is connected for AutoStore operation
(system V
on V
the STK12C68 will attempt to pull HSB low; if HSB
doesn’t actually get below V
ing to pull HSB low and abort the
HARDWARE PROTECT
The STK12C68 offers hardware protection against
inadvertent
ing low-voltage conditions. When V
externally initiated
WRITE
AutoStore can be completely disabled by tying V
to ground and applying + 5V to V
AutoStore
initiated by explicit request using either the software
sequence or the HSB pin.
LOW AVERAGE ACTIVE POWER
The STK12C68 draws significantly less current
when it is cycled at times longer than 50ns. Figure 5
shows the relationship between I
time. Worst-case current consumption is shown for
both
perature range, V
enable). Figure 6 shows the same relationship for
WRITE
than 100%, only standby current is drawn when the
chip is disabled. The overall average current drawn
by the STK12C68 depends on the following items:
1)
chip enable; 3) the overall cycle rate for accesses;
4) the ratio of
temperature; 6) the V
CMOS
CAP
STORE
CMOS
s are inhibited.
cycles. If the chip enable duty cycle is less
) and V
Inhibit mode; in this mode,
STK12C68 (SMD5962-94599)
CC
vs.
STORE
and
connected to V
function can be disabled on the fly by
OH
TTL
CC
READ
of at least 2.2V, as it will have to
TTL
CC
crosses V
input levels; 2) the duty cycle of
operation and
= 5.5V, 100% duty cycle on chip
STORE
s to
cc
input levels (commercial tem-
level; and 7) I/O loading.
WRITE
CCX
SWITCH
IL
operations and
, the part will stop try-
and a 68μF capacitor
s; 5) the operating
CC
STORE
SRAM WRITE
on the way down,
STORE
CAP
CAP
and
STORE
. This is the
< V
READ
attempt.
s are only
SWITCH
. When
s dur-
SRAM
cycle
, all
CCX