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CY7C2665KV18 Datasheet(PDF) 7 Page - Cypress Semiconductor |
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CY7C2665KV18 Datasheet(HTML) 7 Page - Cypress Semiconductor |
7 / 31 page CY7C2663KV18, CY7C2665KV18 Document Number: 001-44141 Rev. *K Page 7 of 31 specified location. Therefore, write accesses to the device can not 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 deselected, the write port ignores all inputs after the pending write operations have been completed. Byte Write Operations Byte write operations are supported by the CY7C2663KV18. A write operation is initiated as described in the section Write Operations on page 6. 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 BWS input during the data portion of a write latches the data being presented and writes it into the device. Deasserting the BWS input during the data portion of a write enables the data stored in the device for that byte to remain unaltered. This feature can be used to simplify read, modify, or write operations to a byte write operation. Concurrent Transactions The read and write ports on the CY7C2663KV18 operate completely independently of one another. As each port latches the address inputs on different clock edges, the user can read or write to any location, regardless of the transaction on the other port. If the ports access the same location when a read follows a write in successive clock cycles, the SRAM delivers the most recent information associated with the specified address location. This includes forwarding data from a write cycle that was initiated on the previous K clock rise. Read access and write access must be scheduled such that one transaction is initiated on any clock cycle. If both ports are selected on the same K clock rise, the arbitration depends on the previous state of the SRAM. If both ports are deselected, the read port takes priority. If a read was initiated on the previous cycle, the write port takes priority (as read operations can not be initiated on consecutive cycles). If a write was initiated on the previous cycle, the read port takes priority (as write operations can not be initiated on consecutive cycles). Therefore, asserting both port selects active from a deselected state results in alter- nating read or write operations being initiated, with the first access being a read. Depth Expansion The CY7C2663KV18 has a port select input for each port. This enables for easy depth expansion. Both port selects are sampled on the rising edge of the positive input clock only (K). Each port select input can deselect the specified port. Deselecting a port does not affect the other port. All pending transactions (read and write) are completed before the device is deselected. Programmable Impedance An external resistor, RQ, must be connected between the ZQ pin on the SRAM and VSS to allow 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 VDDQ =1.5 V. The output impedance is adjusted every 1024 cycles upon power-up to account for drifts in supply voltage and temperature. Echo Clocks Echo clocks are provided on the QDR II+ to simplify data capture on high-speed systems. Two echo clocks are generated by the QDR II+. CQ is referenced with respect to K and CQ is referenced with respect to K. These are free-running clocks and are synchronized to the input clock of the QDR II+. The timing for the echo clocks is shown in the Switching Characteristics on page 24. Valid Data Indicator (QVLD) QVLD is provided on the QDR II+ to simplify data capture on high-speed systems. The QVLD is generated by the QDR II+ device along with data output. This signal is also edge-aligned with the echo clock and follows the timing of any data pin. This signal is asserted half a cycle before valid data arrives. On-Die Termination (ODT) These devices have an ODT feature for data inputs (D[x:0]), byte write selects (BWS[x:0]), and input clocks (K and K). The termination resistors are integrated within the chip. The ODT range selection is enabled through ball R6 (ODT pin). The ODT termination tracks value of RQ where RQ is the resistor tied to the ZQ pin. ODT range selection is made during power-up initialization. A low on this pin selects a low range that follows RQ/3.33 for 175 < RQ < 350 (where RQ is the resistor tied to ZQ pin) A HIGH on this pin selects a high range that follows RQ/1.66 for 175 < RQ < 250 (where RQ is the resistor tied to ZQ pin). When left floating, a high range termination value is selected by default. For a detailed description of ODT implementation, refer to the application note, AN42468, On-Die Termination for QDRII+/DDRII+ SRAMs. 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 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 QDR I mode (with one cycle latency and a longer access time). |
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