Functional overview – Cypress CY7C1446AV33 User Manual

Page 8

CY7C1440AV33
CY7C1442AV33
CY7C1446AV33

Document #: 38-05383 Rev. *E

Page 8 of 31

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 (t

) is 2.6ns

(250-MHz device).

The CY7C1440AV33/CY7C1442AV33/CY7C1446AV33
supports secondary cache in systems utilizing either a linear
or interleaved 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 deter-
mined 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 (BW

) 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 (CE

, CE

) and an

asynchronous Output Enable (OE) provide for easy bank
selection and output tri-state control. ADSP is ignored if CE

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) CE

, CE

are all asserted active, and (3) the Write

signals (GW, BWE) are all deserted HIGH. ADSP is ignored if
CE

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) CE

, CE

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 BW

) 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 BW

signals.

The CY7C1440AV33/CY7C1442AV33/CY7C1446AV33
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 (BW

) 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.

Because CY7C1440AV33/CY7C1442AV33/CY7C1446AV33
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) CE

, CE

are all asserted active, and

(4) the appropriate combination of the Write inputs (GW, BWE,
and BW

) 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.

Burst Sequences

The CY7C1440AV33/CY7C1442AV33/CY7C1446AV33
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 automati-
cally increment the burst counter to the next address in the
burst sequence. Both Read and Write burst operations are
supported.

Sleep Mode

The ZZ input pin is an asynchronous input. Asserting ZZ
places the SRAM in a power conservation “sleep” mode. Two
clock cycles are required to enter into or exit from this “sleep”
mode. While in this mode, data integrity is guaranteed.
Accesses pending when entering the “sleep” mode are not
considered valid nor is the completion of the operation
guaranteed. The device must be deselected prior to entering
the “sleep” mode. CE

, CE

, ADSP, and ADSC must

remain inactive for the duration of t

ZZREC

after the ZZ input

returns LOW.

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