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CY7C1321KV18-333BZC Datasheet(PDF) 10 Page - Cypress Semiconductor |
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CY7C1321KV18-333BZC Datasheet(HTML) 10 Page - Cypress Semiconductor |
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10 / 33 page  CY7C1317KV18, CY7C1917KV18 CY7C1319KV18, CY7C1321KV18 Document Number: 001-58906 Rev. *C Page 10 of 33 register until the next write cycle occurs. On the first write cycle after the read(s), the stored data from the earlier write is written into the SRAM array. This is called a posted write. If a read is performed on the same address on which a write is performed in the previous cycle, the SRAM reads out the most current data. The SRAM does this by bypassing the memory array and reading the data from the registers. Depth Expansion Depth expansion requires replicating the LD control signal for each bank. All other control signals can be common between banks as appropriate. Programmable Impedance An external resistor, RQ, must be connected between the ZQ pin on the SRAM and VSS to enable the SRAM to adjust its output driver impedance. The value of RQ must be 5 × the value of the intended line impedance driven by the SRAM. The allowable range of RQ to guarantee impedance matching with a tolerance of ±15% is between 175 and 350 , with V DDQ = 1.5 V. The output impedance is adjusted every 1024 cycles at power up to account for drifts in supply voltage and temperature. Echo Clocks Echo clocks are provided on the DDR II to simplify data capture on high speed systems. Two echo clocks are generated by the DDR II. CQ is referenced with respect to C and CQ is referenced with respect to C. These are free running clocks and are synchronized to the output clock of the DDR II. In the single clock mode, CQ is generated with respect to K and CQ is generated with respect to K. The timing for the echo clocks is shown in Switching Characteristics on page 26. PLL These chips use a PLL that is designed to function between 120 MHz and the specified maximum clock frequency. During power up, when the DOFF is tied HIGH, the PLL is locked after 20 s of stable clock. The PLL can also be reset by slowing or stopping the input clocks K and K for a minimum of 30 ns. However, it is not necessary to reset the PLL to lock it to the desired frequency. The PLL automatically locks 20 s after a stable clock is presented. The PLL may be disabled by applying ground to the DOFF pin. When the PLL is turned off, the device behaves in DDR I mode (with one cycle latency and a longer access time). [+] Feedback |
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