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STK14C88-3 Datasheet(PDF) 12 Page - Simtek Corporation |
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STK14C88-3 Datasheet(HTML) 12 Page - Simtek Corporation |
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12 / 18 page  12 Feb, 2008 Document Control #ML0015 Rev 2.0 STK14C88-3 HSB OPERATION The STK14C88-3 provides the HSB pin for control- ling and acknowledging the STORE operations. The HSB pin can be used to request a hardware STORE cycle. When the HSB pin is driven low, the STK14C88-3 will conditionally initiate a STORE oper- ation 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 has a very resistive pullup and 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 VCAP if HSB is used as a driver. 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 STK14C88-3 will continue SRAM operations for t DELAY. 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, 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 STK14C88-3s 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 STK14C88-3s. An external pull-up resistor to +3.3V is required since HSB acts as an open drain pull- down. The V CAP pins from the other STK14C88-3 parts can be tied together and share a single capac- itor. The capacitor size must be scaled by the num- ber of devices connected to it. When any one of the STK14C88-3s 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 STK14C88-3s that have been written since the last nonvolatile cycle). During any STORE operation, regardless of how it was initiated, the STK14C88-3 will continue to drive the HSB pin low, releasing it only when the STORE is complete. Upon completion of the STORE operation the STK14C88-3 will remain disabled until the HSB pin returns high. If HSB is not used, it should be left unconnected. BEST PRACTICES nvSRAM products have been used effectively for over 15 years. While ease-of-use is one of the prod- uct’s main system values, experience gained work- ing with hundreds of applications has resulted in the following suggestions as best practices: • The non-volatile cells in an nvSRAM are pro- grammed on the test floor during final test and quality assurance. Incoming inspection routines at customer or contract manufacturer’s sites will sometimes reprogram these values. Final NV pat- terns are typically repeating patterns of AA, 55, 00, FF, A5, or 5A. End product’s firmware should not assume an NV array is in a set programmed state. Routines that check memory content val- ues to determine first time system configuration, cold or warm boot status, etc. should always pro- gram a unique NV pattern (e.g., complex 4-byte pattern of 46 E6 49 53 hex or more random bytes) as part of the final system manufacturing test to ensure these system routines work consis- tently. • Power up boot firmware routines should rewrite the nvSRAM into the desired state (autostore enabled, etc.). While the nvSRAM is shipped in a preset state, best practice is to again rewrite the nvSRAM into the desired state as a safeguard against events that might flip the bit inadvertently (program bugs, incoming inspection routines, etc.). •The Vcap value specified in this datasheet includes a minimum and a maximum value size. Best practice is to meet this requirement and not exceed the max Vcap value because the nvSRAM internal algorithm calculates Vcap charge time based on this max Vcap value. Customers that want to use a larger Vcap value to make sure there is extra store charge and store time should discuss their Vcap size selection with Simtek to understand any impact on the Vcap voltage level at the end of a tRECALL period. |
Similar Part No. - STK14C88-3_08 |
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Similar Description - STK14C88-3_08 |
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