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CY7C1523KV18 Datasheet(PDF) 9 Page - Cypress Semiconductor |
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CY7C1523KV18 Datasheet(HTML) 9 Page - Cypress Semiconductor |
9 / 31 page CY7C1522KV18, CY7C1529KV18 CY7C1523KV18, CY7C1524KV18 Document Number: 001-00438 Rev. *I Page 9 of 31 Functional Overview The CY7C1522KV18, CY7C1529KV18, CY7C1523KV18, and CY7C1524KV18 are synchronous pipelined Burst SRAMs equipped with a DDR II Separate I/O interface, which operates with a read latency of one and half cycles when DOFF pin is tied HIGH. When DOFF pin is set LOW or connected to VSS the device behaves in DDR-I mode with a read latency of one clock cycle. Accesses are initiated on the rising edge of the positive input clock (K). All synchronous input timing is referenced from the rising edge of the input clocks (K and K) and all output timing is referenced to the rising edge of the output clocks (C/C, or K/K when in single clock mode). All synchronous data inputs (D[x:0]) pass through input registers controlled by the rising edge of the input clocks (K and K). All synchronous data outputs (Q[x:0]) pass through output registers controlled by the rising edge of the output clocks (C/C, or K/K when in single-clock mode). All synchronous control (R/W, LD, BWS[0:X]) inputs pass through input registers controlled by the rising edge of the input clock (K). CY7C1523KV18 is described in the following sections. The same basic descriptions apply to CY7C1522KV18, CY7C1529KV18, and CY7C1524KV18. Read Operations The CY7C1523KV18 is organized internally as two arrays of 1 M × 18. Accesses are completed in a burst of two sequential 18-bit data words. Read operations are initiated by asserting R/W HIGH and LD LOW at the rising edge of the positive input clock (K). The address presented to address inputs is stored in the read address register. Following the next K clock rise the corresponding lowest order 18-bit word of data is driven onto the Q[17:0] using C as the output timing reference. On the subsequent rising edge of C, the next 18-bit data word is driven onto the Q[17:0]. The requested data is valid 0.45 ns from the rising edge of the output clock (C or C, or K and K when in single clock mode, for 200 MHz and 250 MHz device). Read accesses can be initiated on every rising edge of the positive input clock (K). This pipelines the data flow such that data is transferred out of the device on every rising edge of the output clocks, C/C (or K/K when in single clock mode). The CY7C1523KV18 first completes the pending read transactions, when read access is deselected. Synchronous internal circuitry automatically tristates the output following the next rising edge of the positive output clock (C). 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. 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. The 36 bits of data are then written into the memory array at the specified location. Write accesses can be initiated on every rising edge of the positive input clock (K). This 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 CY7C1523KV18. 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, and write operations to a byte write operation. Single Clock Mode The CY7C1523KV18 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 CY7C1523KV18 enables high performance operation through high clock frequencies (achieved through pipelining) and double data rate mode of operation. 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. 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 VDDQ =1.5 V. The output impedance is adjusted every 1024 cycles at power up to account for drifts in supply voltage and temperature. [+] Feedback |
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