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CY7C1321KV18-333BZC Datasheet(PDF) 7 Page - Cypress Semiconductor |
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CY7C1321KV18-333BZC Datasheet(HTML) 7 Page - Cypress Semiconductor |
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7 / 31 page  CY7C1319KV18, CY7C1321KV18 Document Number: 001-58906 Rev. *E Page 7 of 31 Write Operations Write operations are initiated by asserting R/W LOW and LD LOW at the rising edge of the positive input clock (K). The address presented to address inputs is stored in the write address register and the least two significant bits of the address are presented to the burst counter. The burst counter increments the address in a linear fashion. On the following K clock rise the data presented to D[17:0] is latched and stored into the 18-bit write data register, provided BWS[1:0] are both asserted active. On the subsequent rising edge of the negative input clock (K) the information presented to D[17:0] is also stored into the write data register, provided BWS[1:0] are both asserted active. This process continues for one more cycle until four 18-bit words (a total of 72 bits) of data are stored in the SRAM. The 72 bits of data are then written into the memory array at the specified location. Therefore, Write accesses to the device cannot be initiated on two consecutive K clock rises. The internal logic of the device ignores the second write request. Write accesses can be initiated on every other rising edge of the positive input clock (K). Doing so pipelines the data flow such that 18 bits of data can be transferred into the device on every rising edge of the input clocks (K and K). When Write access is deselected, the device ignores all inputs after the pending write operations are completed. Byte Write Operations Byte write operations are supported by the CY7C1319KV18. A write operation is initiated as described in the Write Operations section. The bytes that are written are determined by BWS0 and BWS1, which are sampled with each set of 18-bit data words. Asserting the appropriate Byte Write Select input during the data portion of a write latches the data being presented and writes it into the device. Deasserting the Byte Write Select input during the data portion of a write enables the data stored in the device for that byte to remain unaltered. This feature is used to simplify read/modify/write operations to a byte write operation. Single Clock Mode The CY7C1319KV18 is used with a single clock that controls both the input and output registers. In this mode the device recognizes only a single pair of input clocks (K and K) that control both the input and output registers. This operation is identical to the operation if the device had zero skew between the K/K and C/C clocks. All timing parameters remain the same in this mode. To use this mode of operation, tie C and C HIGH at power on. This function is a strap option and not alterable during device operation. DDR Operation The CY7C1319KV18 enables high-performance operation through high clock frequencies (achieved through pipelining) and double data rate mode of operation. The CY7C1319KV18 requires a single No Operation (NOP) cycle when transitioning from a read to a write cycle. At higher frequencies, some applications may require a second NOP cycle to avoid contention. If a read occurs after a write cycle, address and data for the write are stored in registers. The write information must be stored because the SRAM cannot perform the last word write to the array without conflicting with the read. The data stays in this 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 24. 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). |
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