CY7C1461AV25
CY7C1463AV25
CY7C1465AV25
Document #: 38-05355 Rev. *E
Page 9 of 29
Functional Overview
The CY7C1461AV25/CY7C1463AV25/CY7C1465AV25 is a
synchronous flow-through burst SRAM designed specifically
to eliminate wait states during Write-Read transitions. All
synchronous inputs pass through input registers controlled by
the rising edge of the clock. The clock signal is qualified with
the Clock Enable input signal (CEN). If CEN is HIGH, the clock
signal is not recognized and all internal states are maintained.
All synchronous operations are qualified with CEN. Maximum
access delay from the clock rise (tCDV) is 6.5 ns (133-MHz
device).
Accesses can be initiated by asserting all three Chip Enables
(CE1, CE2, CE3) active at the rising edge of the clock. If Clock
Enable (CEN) is active LOW and ADV/LD is asserted LOW,
the address presented to the device will be latched. The
access can either be a read or write operation, depending on
the status of the Write Enable (WE). BWX can be used to
conduct byte write operations.
Write operations are qualified by the Write Enable (WE). All
writes are simplified with on-chip synchronous self-timed write
circuitry.
Three synchronous Chip Enables (CE1, CE2, CE3) and an
asynchronous Output Enable (OE) simplify depth expansion.
All operations (Reads, Writes, and Deselects) are pipelined.
ADV/LD should be driven LOW once the device has been
deselected in order to load a new address for the next
operation.
Single Read Accesses
A read access is initiated when the following conditions are
satisfied at clock rise: (1) CEN is asserted LOW, (2) CE1, CE2,
and CE3 are ALL asserted active, (3) the Write Enable input
signal WE is deasserted HIGH, and (4) ADV/LD is asserted
LOW. The address presented to the address inputs is latched
into the Address Register and presented to the memory array
and control logic. The control logic determines that a read
access is in progress and allows the requested data to
propagate to the output buffers. The data is available within 6.5
ns (133-MHz device) provided OE is active LOW. After the first
clock of the read access, the output buffers are controlled by
OE and the internal control logic. OE must be driven LOW in
order for the device to drive out the requested data. On the
subsequent clock, another operation (Read/Write/Deselect)
can be initiated. When the SRAM is deselected at clock rise
by one of the chip enable signals, its output will be tri-stated
immediately.
Burst Read Accesses
The CY7C1461AV25/CY7C1463AV25/CY7C1465AV25 has
an on-chip burst counter that allows the user the ability to
supply a single address and conduct up to four Reads without
reasserting the address inputs. ADV/LD must be driven LOW
in order to load a new address into the SRAM, as described in
the Single Read Access section above. The sequence of the
burst counter is determined by the MODE input signal. A LOW
input on MODE selects a linear burst mode, a HIGH selects an
interleaved burst sequence. Both burst counters use A0 and
A1 in the burst sequence, and will wrap around when incre-
mented sufficiently. A HIGH input on ADV/LD will increment
the internal burst counter regardless of the state of chip enable
inputs or WE. WE is latched at the beginning of a burst cycle.
Therefore, the type of access (Read or Write) is maintained
throughout the burst sequence.
Single Write Accesses
Write access are initiated when the following conditions are
satisfied at clock rise: (1) CEN is asserted LOW, (2) CE1, CE2,
and CE3 are ALL asserted active, and (3) the write signal WE
is asserted LOW. The address presented to the address bus
is loaded into the Address Register. The write signals are
latched into the Control Logic block. The data lines are
automatically tri-stated regardless of the state of the OE input
signal. This allows the external logic to present the data on
DQs and DQPX.
On the next clock rise the data presented to DQs and DQPX
(or a subset for byte write operations, see truth table for
details) inputs is latched into the device and the write is
complete. Additional accesses (Read/Write/Deselect) can be
initiated on this cycle.
The data written during the Write operation is controlled by BWX
signals. The CY7C1461AV25/CY7C1463AV25/CY7C1465AV25
provides byte write capability that is described in the truth table.
Asserting the Write Enable input (WE) with the selected Byte
Write Select input will selectively write to only the desired
bytes. Bytes not selected during a byte write operation will
remain unaltered. A synchronous self-timed write mechanism
has been provided to simplify the write operations. Byte write
capability has been included in order to greatly simplify
Read/Modify/Write sequences, which can be reduced to
simple byte write operations.
Because the CY7C1461AV25/CY7C1463AV25/CY7C1465AV25
is a common I/O device, data should not be driven into the
device while the outputs are active. The Output Enable (OE)
can be deasserted HIGH before presenting data to the DQs
and DQPX inputs. Doing so will tri-state the output drivers. As
a safety precaution, DQs and DQPX are automatically
tri-stated during the data portion of a write cycle, regardless of
the state of OE.
Burst Write Accesses
The CY7C1461AV25/CY7C1463AV25/CY7C1465AV25 has
an on-chip burst counter that allows the user the ability to
supply a single address and conduct up to four Write opera-
tions without reasserting the address inputs. ADV/LD must be
driven LOW in order to load the initial address, as described
in the Single Write Access section above. When ADV/LD is
driven HIGH on the subsequent clock rise, the Chip Enables
(CE1, CE2, and CE3) and WE inputs are ignored and the burst
counter is incremented. The correct BWX inputs must be
driven in each cycle of the burst write, in order to write the
correct bytes of data.
Interleaved Burst Address Table
(MODE = Floating or VDD)
First
Address
A1: A0
Second
Address
A1: A0
Third
Address
A1: A0
Fourth
Address
A1: A0
00
01
10
11
01
00
11
10
10
11
00
01
11
10
01
00
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