CY7C1440AV25
CY7C1442AV25
CY7C1446AV25
Document #: 38-05350 Rev. *E
Page 8 of 32
Functional Overview
All synchronous inputs pass through input registers controlled
by the rising edge of the clock. All data outputs pass through
output registers controlled by the rising edge of the clock.
Maximum access delay from the clock rise (tCO) is 2.6 ns
(250-MHz device).
The CY7C1440AV25/CY7C1442AV25/CY7C1446AV25 supports
secondary cache in systems utilizing either a linear or inter-
leaved burst sequence. The interleaved burst order supports
Pentium and i486
™ processors. The linear burst sequence is
suited for processors that utilize a linear burst sequence. The
burst order is user selectable, and is determined by sampling
the MODE input. Accesses can be initiated with either the
Processor Address Strobe (ADSP) or the Controller Address
Strobe (ADSC). Address advancement through the burst
sequence is controlled by the ADV input. A two-bit on-chip
wraparound burst counter captures the first address in a burst
sequence and automatically increments the address for the
rest of the burst access.
Byte Write operations are qualified with the Byte Write Enable
(BWE) and Byte Write Select (BWX) inputs. A Global Write
Enable (GW) overrides all Byte Write inputs and writes data to
all four bytes. All writes are simplified with on-chip
synchronous self-timed Write circuitry.
Three synchronous Chip Selects (CE1, CE2, CE3) and an
asynchronous Output Enable (OE) provide for easy bank
selection and output tri-state control. ADSP is ignored if CE1
is HIGH.
Single Read Accesses
This access is initiated when the following conditions are
satisfied at clock rise: (1) ADSP or ADSC is asserted LOW, (2)
CE1, CE2, CE3 are all asserted active, and (3) the Write
signals (GW, BWE) are all deserted HIGH. ADSP is ignored if
CE1 is HIGH. The address presented to the address inputs (A)
is stored into the address advancement logic and the Address
Register while being presented to the memory array. The
corresponding data is allowed to propagate to the input of the
Output Registers. At the rising edge of the next clock the data
is allowed to propagate through the output register and onto
the data bus within 2.6 ns (250-MHz device) if OE is active
LOW. The only exception occurs when the SRAM is emerging
from a deselected state to a selected state, its outputs are
always tri-stated during the first cycle of the access. After the
first cycle of the access, the outputs are controlled by the OE
signal. Consecutive single Read cycles are supported. Once
the SRAM is deselected at clock rise by the chip select and
either ADSP or ADSC signals, its output will tri-state immedi-
ately.
Single Write Accesses Initiated by ADSP
This access is initiated when both of the following conditions
are satisfied at clock rise: (1) ADSP is asserted LOW, and
(2) CE1, CE2, CE3 are all asserted active. The address
presented to A is loaded into the address register and the
address advancement logic while being delivered to the
memory array. The Write signals (GW, BWE, and BWX) and
ADV inputs are ignored during this first cycle.
ADSP-triggered Write accesses require two clock cycles to
complete. If GW is asserted LOW on the second clock rise, the
data presented to the DQs inputs is written into the corre-
sponding address location in the memory array. If GW is HIGH,
then the Write operation is controlled by BWE and BWX
signals.
The CY7C1440AV25/CY7C1442AV25/CY7C1446AV25 provides
Byte Write capability that is described in the Write Cycle
Descriptions table. Asserting the Byte Write Enable input
(BWE) with the selected Byte Write (BWX) input, will selec-
tively 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.
Because CY7C1440AV25/CY7C1442AV25/CY7C1446AV25
is a common I/O device, the Output Enable (OE) must be
deasserted HIGH before presenting data to the DQs inputs.
Doing so will tri-state the output drivers. As a safety
precaution, DQs are automatically tri-stated whenever a Write
cycle is detected, regardless of the state of OE.
Single Write Accesses Initiated by ADSC
ADSC Write accesses are initiated when the following condi-
tions are satisfied: (1) ADSC is asserted LOW, (2) ADSP is
deserted HIGH, (3) CE1, CE2, CE3 are all asserted active, and
(4) the appropriate combination of the Write inputs (GW, BWE,
and BWX) are asserted active to conduct a Write to the desired
byte(s). ADSC-triggered Write accesses require a single clock
cycle to complete. The address presented to A is loaded into
the address register and the address advancement logic while
being delivered to the memory array. The ADV input is ignored
during this cycle. If a global Write is conducted, the data
presented to the DQs is written into the corresponding address
location in the memory core. If a Byte Write is conducted, only
the selected bytes are written. 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.
Because CY7C1440AV25/CY7C1442AV25/CY7C1446AV25
is a common I/O device, the Output Enable (OE) must be
deasserted HIGH before presenting data to the DQs inputs.
Doing so will tri-state the output drivers. As a safety
precaution, DQs are automatically tri-stated whenever a Write
cycle is detected, regardless of the state of OE.
Burst Sequences
The CY7C1440AV25/CY7C1442AV25/CY7C1446AV25 provides
a two-bit wraparound counter, fed by A1: A0, that implements
either an interleaved or linear burst sequence. The interleaved
burst sequence is designed specifically to support Intel
Pentium applications. The linear burst sequence is designed
to support processors that follow a linear burst sequence. The
burst sequence is user selectable through the MODE input.
Asserting ADV LOW at clock rise will automatically increment
the burst counter to the next address in the burst sequence.
Both Read and Write burst operations are supported.
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