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STK12C68-CF25 参数 Datasheet PDF下载

STK12C68-CF25图片预览
型号: STK12C68-CF25
PDF下载: 下载PDF文件 查看货源
内容描述: 8Kx8自动存储的nvSRAM [8Kx8 AutoStore nvSRAM]
分类和应用: 存储静态存储器
文件页数/大小: 20 页 / 526 K
品牌: SIMTEK [ SIMTEK CORPORATION ]
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STK12C68 (SMD5962-94599)  
If HSB is not used, it should be left unconnected.  
HSB OPERATION  
The STK12C68 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 STK12C68 will  
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 STK12C68 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 STK12C68 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.  
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 STK12C68 will  
HARDWARE PROTECT  
The STK12C68 offers hardware protection against  
inadvertent STORE operation and SRAM WRITEs dur-  
ing low-voltage conditions. When VCAP < VSWITCH, all  
externally initiated STORE operations and SRAM  
WRITEs are inhibited.  
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.  
AutoStore can be completely disabled by tying VCCX  
to ground and applying + 5V to VCAP . This is the  
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 VCAP pins from the other STK12C68 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  
STK12C68s 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  
STK12C68s that have been written since the last  
nonvolatile cycle).  
AutoStore  
Inhibit mode; in this mode, STOREs are only  
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 ICC and READ cycle  
time. Worst-case current consumption is shown for  
both CMOS and TTL input levels (commercial tem-  
perature range, VCC = 5.5V, 100% duty cycle on chip  
enable). Figure 6 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 STK12C68 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 READs to WRITEs; 5) the operating  
During any STORE operation, regardless of how it  
was initiated, the STK12C68 will continue to drive  
the HSB pin low, releasing it only when the STORE is  
complete. Upon completion of the STORE operation  
the STK12C68 will remain disabled until the HSB  
pin returns high.  
temperature; 6) the V level; and 7) I/O loading.  
cc  
Rev 0.7  
Document Control #ML0008  
February 2007  
11