STK22C48
least one
WRITE
operation has taken place since the
most recent
STORE
or
RECALL
cycle.
If the power supply drops faster than 20
μs/volt
before V
CCX
reaches V
SWITCH
, then a 2.2 ohm resistor
should be inserted between V
CCX
and the system
supply to avoid momentary excess of current
between Vccx and Vcap.
operate in this mode the HSB pin should be con-
nected together to the HSB pins from the other
STK22C48s. An external pull-up resistor to + 5V is
required since HSB acts as an open drain pull down.
The V
CAP
pins from the other STK22C48 parts can
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
STK22C48s detects a power loss and asserts HSB,
the common HSB pin will cause all parts to request a
STORE
cycle (a
STORE
will take place in those
STK22C48s that have been written since the last
nonvolatile cycle).
During any
STORE
operation, regardless of how it
was initiated, the STK22C48 will continue to drive
the HSB pin low, releasing it only when the
STORE
is
complete. Upon completion of the
STORE
operation
the STK22C48 will remain disabled until the HSB pin
returns high.
If HSB is not used, it should be left unconnected.
HSB OPERATION
The STK22C48 provides the HSB pin for controlling
and acknowledging the
STORE
operations. The HSB
pin is used to request a hardware
STORE
cycle.
When the HSB pin is driven low, the STK22C48 will
conditionally initiate a
STORE
operation after t
DELAY
;
an actual
STORE
cycle will only begin if a
WRITE
to
the
SRAM
took place since the last
STORE
or
RECALL
cycle. The HSB pin acts as an open drain
driver that is internally driven low to indicate a busy
condition while the
STORE
(initiated by any means)
is in progress. Pull up this pin with an external 10K
ohm resistor to V
CAP
if HSB is used as a driver.
SRAM READ
and
WRITE
operations that are in
PREVENTING STORES
The
STORE
function can be disabled on the fly by
holding HSB high with a driver capable of sourcing
30mA at a VOH of at least 2.2V, as it will have to
overpower the internal pull-down device that drives
HSB low for 20μs at the onset of a
STORE
. When the
STK22C48 is connected for AutoStore operation
(system V
CC
connected to V
CCX
and a 68μF capacitor
on V
CAP
) and V
CC
crosses V
SWITCH
on the way down,
the STK22C48 will attempt to pull HSB low; if HSB
doesn’t actually get below V
IL
, the part will stop try-
ing to pull HSB low and abort the
STORE
attempt.
progress when HSB is driven low by any means are
given time to complete before the
STORE
operation
is initiated. After HSB goes low, the STK22C48 will
continue
SRAM
operations for t
DELAY
. During t
DELAY
,
multiple
SRAM READ
operations may take place. If a
WRITE
is in progress when HSB is pulled low it will
be allowed a time, t
DELAY
, to complete. However, any
SRAM WRITE
cycles requested after HSB goes low
will be inhibited until HSB returns high.
The HSB pin can be used to synchronize multiple
STK22C48s while using a single larger capacitor. To
10kΩ∗
0.1μF
Bypass
10kΩ∗
10kΩ
1
32
31
30
10kΩ∗
1
32
31
30
16
17
1
32
31
30
68μF
6v, ±20%
+
0.1μF
Bypass
0.1μF
Bypass
16
16
17
17
Figure 2: AutoStore Mode
Figure 3: System Power Mode
Figure 4: AutoStore
Inhibit Mode
*If HSB is not used, it should be left unconnected.
Document Control #ML0004 Rev 0.3
February 2007
9
10kΩ
10kΩ
SIMTEK [ SIMTEK CORPORATION ]
