Functional Overview
The CY7C1510KV18, CY7C1525KV18, CY7C1512KV18, and CY7C1514KV18 are synchronous pipelined Burst SRAMs with a read port and a write port. The read port is dedicated to read operations and the write port is dedicated to write operations. Data flows into the SRAM through the write port and flows out through the read port. These devices multiplex the address inputs to minimize the number of address pins required. By having separate read and write ports, the QDR-II completely eliminates the need to turn around the data bus and avoids any possible data contention, thereby simplifying system design. Each access consists of two 8-bit data transfers in the case of CY7C1510KV18, two 9-bit data transfers in the case of CY7C1525KV18, two 18-bit data transfers in the case of CY7C1512KV18, and two 36-bit data transfers in the case of CY7C1514KV18 in one clock cycle.
This device 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 then the device behaves in QDR-I mode with a read latency of one clock cycle.
Accesses for both ports are initiated on the rising edge of the positive input clock (K). All synchronous input timing is refer- enced from the rising edge of the input clocks (K and K) and all output timing is referenced to the output clocks (C and C, or K and K when in single clock mode).
All synchronous data inputs (D[x:0]) pass through input registers controlled by 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 and C, or K and K when in single clock mode).
All synchronous control (RPS, WPS, BWS[x:0]) inputs pass through input registers controlled by the rising edge of the input clocks (K and K).
CY7C1512KV18 is described in the following sections. The same basic descriptions apply to CY7C1510KV18, CY7C1525KV18, and CY7C1514KV18.
Read Operations
The CY7C1512KV18 is organized internally as two arrays of 2M x 18. Accesses are completed in a burst of two sequential 18-bit data words. Read operations are initiated by asserting RPS active at the rising edge of the positive input clock (K). The address is latched on the rising edge of the K clock. The address presented to the 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 and C or K and K when in single clock mode).
Synchronous internal circuitry automatically tristates the outputs following the next rising edge of the output clocks (C/C). This enables for a seamless transition between devices without the insertion of wait states in a depth expanded memory.
Write Operations
Write operations are initiated by asserting WPS active at the rising edge of the positive input clock (K). On the same K clock rise the data presented to D[17:0] is latched and stored into the
lower 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 address is latched and 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.
When deselected, the write port ignores all inputs after the pending write operations are completed.
Byte Write Operations
Byte write operations are supported by the CY7C1512KV18. 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, or write operations to a byte write operation.
Single Clock Mode
The CY7C1510KV18 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, the user must tie C and C HIGH at power on. This function is a strap option and not alterable during device operation.
Concurrent Transactions
The read and write ports on the CY7C1512KV18 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. The user can start reads and writes in the same clock cycle. If the ports access the same location at the same time, 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.
Depth Expansion
The CY7C1512KV18 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 enable the SRAM to adjust its output driver impedance. The value of RQ must be 5X 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 175Ω and 350Ω, with VDDQ = 1.5V. The output impedance is adjusted every 1024 cycles upon power up to account for drifts in supply voltage and temperature.
