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STK22C48-WF25 Datasheet(PDF) 6 Page - Simtek Corporation |
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STK22C48-WF25 Datasheet(HTML) 6 Page - Simtek Corporation |
6 / 10 page STK25C48 March 2006 6Document Control # ML0005 rev 0.2 The STK25C48 is a versatile memory chip that pro- vides several modes of operation. The STK25C48 can operate as a standard 8K x 8 SRAM. It has an 8K x 8 Nonvolatile Elements shadow to which the SRAM information can be copied, or from which the SRAM can be updated in nonvolatile mode. NOISE CONSIDERATIONS Note that the STK25C48 is a high-speed memory and so must have a high-frequency bypass capaci- tor of approximately 0.1 μF connected between V CC and V SS, using leads and traces that are as short as possible. As with all high-speed CMOS ICs, normal careful routing of power, ground and signals will help prevent noise problems. SRAM READ The STK25C48 performs a READ cycle whenever E and G are low and W is high. The address specified on pins A 0-10 determines which of the 2,048 data bytes will be accessed. When the READ is initiated by an address transition, the outputs will be valid after a delay of t AVQV (READ cycle #1). If the READ is initiated by E or G, the outputs will be valid at t ELQV or at t GLQV, whichever is later (READ cycle #2). The data outputs will repeatedly respond to address changes within the t AVQV access time without the need for tran- sitions on any control input pins, and will remain valid until another address change or until E or G is brought high or W is brought low. SRAM WRITE A WRITE cycle is performed whenever E and W are low. The address inputs must be stable prior to entering the WRITE cycle and must remain stable until either E or W goes high at the end of the cycle. The data on the common I/O pins DQ 0-7 will be writ- ten into the memory if it is valid t DVWH before the end of a W controlled WRITE or t DVEH before the end of an E controlled WRITE. It is recommended that G be kept high during the entire WRITE cycle to avoid data bus contention on the common I/O lines. If G is left low, internal circuitry will turn off the output buffers t WLQZ after W goes low. AutoStore™ OPERATION The STK25C48 uses the intrinsic system capaci- tance to perform an automatic store on power down. As long as the system power supply takes at least t STORE to decay from V SWITCH down to 3.6V, the STK25C48 will safely and automatically store the SRAM data in Nonvolatile Elements on power down. In order to prevent unneeded STORE operations, automatic STORE will be ignored unless at least one WRITE operation has taken place since the most recent STORE or RECALL cycle. POWER-UP RECALL During power up, or after any low-power condition (V CC < VRESET), an internal RECALL request will be latched. When V CC once again exceeds the sense voltage of V SWITCH, a RECALL cycle will automatically be initiated and will take t RESTORE to complete. If the STK25C48 is in a WRITE state at the end of power-up RECALL, the SRAM data will be corrupted. To help avoid this situation, a 10K Ohm resistor should be connected either between W and system V CC or between E and system VCC. HARDWARE PROTECT The STK25C48 offers hardware protection against inadvertent STORE operation and SRAM WRITEs during low-voltage conditions. When V CC < VSWITCH, STORE operations and SRAM WRITEs are inhibited. LOW AVERAGE ACTIVE POWER The STK25C48 draws significantly less current when it is cycled at times longer than 50ns. Figure 2 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 3 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 STK25C48 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 V CC level; and 7) I/O loading. DEVICE OPERATION |
Similar Part No. - STK22C48-WF25 |
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