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STK22C48-NF25 Datasheet(PDF) 9 Page - Simtek Corporation |
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STK22C48-NF25 Datasheet(HTML) 9 Page - Simtek Corporation |
9 / 16 page 9 STK22C48 Feb, 2008 Document Control #ML0004 Rev 2.0 STK22C48 will operate on the stored system charge as power goes down. The user must, however, guar- antee that V CC does not drop below 3.6V during the 10ms STORE cycle. AutoStore INHIBIT MODE If an automatic STORE on power loss is not required, then V CC can be tied to ground and + 5V applied to V CAP (Figure 3). This is the AutoStore Inhibit mode, in which the AutoStore function is disabled. If the STK22C48 is operated in this configuration, refer- ences to V CC should be changed to VCAP throughout this data sheet. In this mode, STORE operations may be triggered with the HSB pin. To enable or disable AutoStore using an IO port pin, see “PREVENTING STORES” on page 9. 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. If the power supply drops faster than 20 μs/volt before V CC reaches VSWITCH, then a 2.2 ohm resistor should be inserted between V CC and the system sup- ply to avoid momentary excess of current between Vcc 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 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 has a very resistive pul- lup 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 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 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. 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 20 μs at the onset of a STORE. When the STK22C48 is connected for AutoStore operation (system V CC connected to VCC and a 68μF capacitor on V CAP) and VCC crosses VSWITCH 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. 17 1 16 32 31 30 Figure 3: AutoStore Inhibit Mode |
Número de pieza similar - STK22C48-NF25 |
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Descripción similar - STK22C48-NF25 |
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