CY7C1261V18
CY7C1276V18
CY7C1263V18
CY7C1265V18
Document Number: 001-06366 Rev. *C
Page 8 of 28
Functional Overview
The CY7C1261V18, CY7C1276V18, CY7C1263V18, and
CY7C1265V18 are synchronous pipelined Burst SRAMs
equipped 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 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 four 8-bit data
transfers in the case of CY7C1261V18, four 9-bit data
transfers in the case of CY7C1276V18, four 18-bit data
transfers in the case of CY7C1263V18, and four 36-bit data
transfers in the case of CY7C1265V18, in two clock cycles.
Accesses for both ports are initiated on the Positive Input
Clock (K). All synchronous input and output timing refer to the
rising edge of the Input clocks (K/K).
All synchronous data inputs (D[x:0]) inputs pass through input
registers controlled by the input clocks (K and K). All
synchronous data outputs (Q[x:0]) outputs pass through output
registers controlled by the rising edge of the Input clocks (K
and K).
All synchronous control (RPS, WPS, BWS[x:0]) inputs pass
through input registers controlled by the rising edge of the
input clocks (K/K).
CY7C1263V18 is described in the following sections. The
same
basic
descriptions
apply
to
CY7C1261V18,
CY7C1276V18, and CY7C1265V18.
Read Operations
The CY7C1263V18 is organized internally as 4 arrays of 512K
x 18. Accesses are completed in a burst of four sequential
18-bit data words. Read operations are initiated by asserting
RPS active at the rising edge of the Positive Input Clock (K).
The addresses presented to address inputs are stored in the
Read address register. Following the next two K clock rising
edges, the corresponding lowest order 18-bit word of data is
driven onto the Q[17:0] using K as the output timing reference.
On the subsequent rising edge of K the next 18-bit data word
is driven onto the Q[17:0]. This process continues until all four
18-bit data words have been driven out onto Q[17:0]. The
requested data is valid 0.45 ns from the rising edge of the Input
clock (K or K). To maintain the internal logic, each read access
must be allowed to complete. Each read access consists of
four 18-bit data words and takes two clock cycles to complete.
Therefore, read accesses to the device cannot be initiated on
two consecutive K clock rises. The internal logic of the device
ignores the second read request. Read accesses can be
initiated on every other K clock rise. Doing so pipelines the
data flow such that data is transferred out of the device on
every rising edge of the input clocks (K and K).
When the read port is deselected, the CY7C1263V18=
completes the pending read transactions. Synchronous
internal circuitry automatically tri-states the outputs following
the next rising edge of the negative Input Clock (K). This
enables 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 following 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 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 trans-
ferred 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 CY7C1263V18. 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 enables the data being
presented to be latched and written 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/write operations to a byte write operation.
Concurrent Transactions
The read and write ports on the CY7C1263V18 operate
completely independently of one another. Because 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 accesses 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 assumes priority (because read
operations cannot be initiated on consecutive cycles). If a write
was initiated on the previous cycle, the read port assumes
priority (because write operations cannot be initiated on
consecutive cycles). Therefore, asserting both port selects
active from a deselected state results in alternating read/write
operations being initiated, with the first access being a read.
Depth Expansion
The CY7C1263V18 has a Port Select input for each port. This
enables easy depth expansion. Both Port Selects are sampled
on the rising edge of the Positive Input Clock only (K). Each
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