STK22C48
least one WRITE operation has taken place since the
most recent STORE or RECALL cycle.
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 VCAP 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).
If the power supply drops faster than 20 μs/volt
before VCCX reaches VSWITCH, then a 2.2 ohm resistor
should be inserted between VCCX and the system
supply to avoid momentary excess of current
between Vccx and Vcap.
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
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.
conditionally initiate a STORE operation after tDELAY
;
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
If HSB is not used, it should be left unconnected.
ohm resistor to V
if HSB is used as a driver.
CAP
PREVENTING STORES
SRAM READ and WRITE operations that are in
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
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 VCC connected to VCCX and a 68μF capacitor
on VCAP) and VCC crosses VSWITCH on the way down,
the STK22C48 will attempt to pull HSB low; if HSB
doesn’t actually get below VIL, the part will stop try-
ing to pull HSB low and abort the STORE attempt.
continue SRAM operations for tDELAY. During tDELAY
,
multiple SRAM READ operations may take place. If a
WRITE is in progress when HSB is pulled low it will
be allowed a time, tDELAY, 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∗
1
1
32
31
30
32
31
30
1
32
31
30
+
16
16
17
17
16
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.
Rev 0.3
Document Control #ML0004
February 2007
9
SIMTEK [ SIMTEK CORPORATION ]
