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CY7C1663KV18 Arkusz danych(PDF) 7 Page - Cypress Semiconductor |
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CY7C1663KV18 Arkusz danych(HTML) 7 Page - Cypress Semiconductor |
7 / 31 page Document Number: 001-44060 Rev. *O Page 7 of 31 CY7C1663KV18/CY7C1665KV18 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 can be used to simplify read, modify, or write operations to a byte write operation. Concurrent Transactions The read and write ports on the CY7C1663KV18 operates 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 alternating read or write operations being initiated, with the first access being a read. Depth Expansion The CY7C1663KV18 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 Connect an external resistor, RQ, 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 five times 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 percent 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. 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). |
Podobny numer części - CY7C1663KV18 |
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Podobny opis - CY7C1663KV18 |
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