CY7C1141V18, CY7C1156V18
CY7C1143V18, CY7C1145V18
Document Number: 001-06583 Rev. *D
Page 8 of 28
Functional Overview
The CY7C1141V18, CY7C1156V18, CY7C1143V18, and
CY7C1145V18 are synchronous pipelined Burst SRAMs
equipped with both 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 in order 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 CY7C1141V18, four 9-bit data transfers in the case of
CY7C1156V18, four 18-bit data transfers in the case of
CY7C1143V18, and four 36-bit data transfers in the case of
CY7C1145V18 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]
) 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 Input clocks (K and K) as well.
All synchronous control (RPS, WPS, BWS
[x:0]
) inputs pass
through input registers controlled by the rising edge of the input
clocks (K/K). CY7C1143V18 is described in the following
sections. The same basic descriptions apply to CY7C1141V18,
CY7C1156V18, and CY7C1145V18.
Read Operations
The CY7C1143V18 is organized internally as four arrays of 256K
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
address presented to Address inputs are stored in the read
address register. Following the next two K clock rise, the corre-
sponding lowest order 18-bit word of data is driven onto the
Q
[17:0]
using K as the output timing reference. On the subse-
quent 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
are 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
internallogic, 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.
Initiate read accesses on every other K clock rise. This 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 CY7C1143V18 first
completes the pending read transactions. Synchronous internal
circuitry automatically tri-states the outputs following the next
rising edge of the Positive Input Clock (K). 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 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. Initiate write
accesses on every other 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 deselected, the write port ignores all inputs after the
pending write operations are completed.
Byte Write Operations
Byte Write operations are supported by the CY7C1143V18. A
write operation is initiated as described in the
Write Operations
.
The bytes that are written are determined by BWS
0
and BWS
1
,
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. Use this feature to
simplify read/modify/write operations to a Byte Write operation.
Concurrent Transactions
The read and write ports on the CY7C1143V18 operate indepen-
dently 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 were deselected, the
read port takes priority. If a read was initiated on the previous
cycle, the write port is based on priority (since read operations
cannot be initiated on consecutive cycles). If a write was initiated
on the previous cycle, the read port is based on priority (since
write operations cannot be initiated on consecutive cycles).
Therefore, asserting both port selects active from a deselected
state results in alternating read/write operations initiated, with the
first access being a read.
[+] Feedback
[+] Feedback
