STK22C48 데이터 시트보기 (PDF) - Unspecified
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STK22C48 Datasheet PDF : 11 Pages
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STK22C48
In order to prevent unneeded STORE operations,
automatic STOREs as well as those initiated by
externally driving HSB low will be ignored unless at
least one WRITE operation has taken place since the
most recent STORE or RECALL cycle. An optional
pull-up resistor is shown connected to HSB. This
can be used to signal the system that the
AutoStore™ cycle is in progress.
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 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.
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
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
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).
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.
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™ opera-
tion (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
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Figure 2: AutoStore™ Mode
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Figure 3: System Power Mode
*If HSB is not used, it should be left unconnected.
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Figure 4: AutoStore™
Inhibit Mode
December 2002
8 Document Control # ML0004 rev 0.0
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