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CY7C1298H
Document #: 38-05665 Rev. *B Page 5 of 16
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.
The CY7C1298H 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 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 (BW
[A:B]
) 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.
Synchronous Chip Selects CE
1
, CE
2
, CE
3
and an
asynchronous Output Enable (OE
) provide for easy bank
selection and output tri-state control. ADSP
is ignored if CE
1
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)
chip selects are all asserted active, and (3) the write signals
(GW
, BWE) are all deasserted HIGH. ADSP is ignored if CE
1
is HIGH. The address presented to the address inputs is
stored into the address advancement logic and the Address
Register while being presented to the memory core. The corre-
sponding 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 t
co
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.
The CY7C1298H is a double-cycle deselect part. Once the
SRAM is deselected at clock rise by the chip select and either
ADSP
or ADSC signals, its output will tri-state immediately
after the next clock rise.
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) chip select is asserted active. The address presented is
loaded into the address register and the address
advancement logic while being delivered to the memory core.
The write signals (GW
, BWE, and BW
[A:B]
) 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 DQx inputs is written into the corre-
sponding address location in the memory core. If GW
is HIGH,
then the write operation is controlled by BWE
and BW
[A:B]
signals. The CY7C1298H provides byte write capability that
is described in the Write Cycle Description table. Asserting the
Byte Write Enable input (BWE) with the selected Byte Write
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 the CY7C1298H is a common I/O device, the Output
Enable (OE
) must be deasserted HIGH before presenting data
to the DQ
inputs. Doing so will tri-state the output drivers. As
a safety precaution, DQ 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
deasserted HIGH, (3) chip select is asserted active, and (4)
the appropriate combination of the write inputs (GW
, BWE,
and BW
[A:B]
) 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 is
loaded into the address register and the address
advancement logic while being delivered to the memory core.
The ADV input is ignored during this cycle. If a global write is
conducted, the data presented to the DQ
X
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 the CY7C1298H is a common I/O device, the Output
Enable (OE) must be deasserted HIGH before presenting data
to the DQ
X
inputs. Doing so will tri-state the output drivers. As
a safety precaution, DQ
X
are automatically tri-stated
whenever a write cycle is detected, regardless of the state of
OE.
Burst Sequences
The CY7C1298H provides a two-bit wraparound counter, fed
by A
[1:0]
, that implements either an interleaved or linear burst
sequence. The interleaved burst sequence is designed specif-
ically 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. Both read and write burst operations
are supported
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.
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
s, ADSP, and ADSC must remain
inactive for the duration of t
ZZREC
after the ZZ input returns
LOW.
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