Cypress CY7C1305BV25 - Manual (Page 5)

CY7C1307BV25
CY7C1305BV25
Document #: 38-05630 Rev. *A Page 5 of 21
Introduction
Functional Overview
The CY7C1305BV25/CY7C1307BV25 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 device completely elimi-
nates the need to “turn-around” the data bus and avoids any
possible data contention, thereby simplifying system design.
Each access consists of four 18-bit data transfers in the case
of CY7C1305BV25 and four 36-bit data transfers in the case
of CY7C1307BV25, in two clock cycles.
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 rising edge of 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 rising edge of 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
[0:x]
) inputs pass
through input registers controlled by the rising edge of input
clocks (K and K).
CY7C1305BV25 is described in the following sections. The
same basic descriptions apply to CY7C1307BV25.
Read Operations
The CY7C1305BV25 is organized internally as 4 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 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]
. This process continues until all four 18-bit data
words have been driven out onto Q
[17:0]
. The requested data
will be valid 2.5 ns from the rising edge of the output clock
(C and C, or K and K when in single clock mode, 250-MHz
device). In order 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 2 clock cycles to
complete. Therefore, Read accesses to the device can not be
initiated on two consecutive K clock rises. The internal logic of
the device will ignore the second Read request. Read
accesses can be initiated on every other K clock rise. Doing
so will pipeline the data flow such that data is transferred out
of the device on every rising edge of the output clocks (C and
C, or K and K when in single clock mode).
When the read port is deselected, the CY7C1305BV25 will first
complete the pending read transactions. Synchronous internal
circuitry will automatically three-state the outputs following the
next rising edge of the positive output clock (C). This will allow
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 can not be initiated on two consecutive
K clock rises. The internal logic of the device will ignore the
second Write request. Write accesses can be initiated on
every other rising edge of the positive clock (K). Doing so will
pipeline 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).
NC/36M N/A Address expansion for 36M. This is not connected to the die. Can be connected to any
voltage level on CY7C1305BV25/CY7C1307BV25.
GND/72M Input Address expansion for 72M. This should be tied LOW on the CY7C1305BV25.
NC/72M N/A Address expansion for 72M. This can be connected to any voltage level on
CY7C1307BV25.
GND/144M Input Address expansion for 144M. This should be tied LOW on
CY7C1305BV25/CY7C1307BV25.
GND/288M Input Address expansion for 144M. This should be tied LOW on CY7C1307BV25.
V
REF
Input-
Reference
Reference Voltage Input. Static input used to set the reference level for HSTL inputs
and Outputs as well as AC measurement points.
V
DD
Power Supply Power supply inputs to the core of the device
V
SS
Ground Ground for the device
V
DDQ
Power Supply Power supply inputs for the outputs of the device
NC N/A Not connected to the die. Can be tied to any voltage level.
Pin Definitions (continued)
Name I/O Description
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