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STK14C88 Datasheet(PDF) 11 Page - Simtek Corporation |
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STK14C88 Datasheet(HTML) 11 Page - Simtek Corporation |
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11 / 19 page  11 STK14C88 February 2007 Document Control #ML0014 Rev 0.3 HSB OPERATION The STK14C88 provides the HSB pin for controlling 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 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 also 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 exter- nal 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 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 STK14C88s 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 STK14C88s. 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 STK14C88 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 STK14C88s 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 STK14C88s that have been written since the last nonvolatile cycle). During any STORE operation, regardless of how it was initiated, the STK14C88 will continue to drive the HSB pin low, releasing it only when the STORE is complete. Upon completion of the STORE operation the STK14C88 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 V OH 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 STK14C88 is connected for AutoStore operation (system V CC connected to VCCX and a 68 μF capacitor on V CAP) and VCC crosses VSWITCH on the way down, the STK14C88 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. HARDWARE PROTECT The STK14C88 offers hardware protection against inadvertent STORE operation and SRAM WRITEs dur- ing low-voltage conditions. When V CAP < VSWITCH, all externally initiated STORE operations and SRAM WRITE s will be inhibited. AutoStore can be completely disabled by tying V CCX to ground and applying + 5V to V CAP. This is the 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 STK14C88 draws significantly less current when it is cycled at times longer than 50ns. Figure 5 shows the relationship between I CC and READ cycle time. Worst-case current consumption is shown for both CMOS and TTL input levels (commercial tem- perature range, V CC = 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 STK14C88 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 temperature; 6) the Vcc level; and 7) I/O loading. |
Similar Part No. - STK14C88 |
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Similar Description - STK14C88 |
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