CY7C024AV/025AV/026AV
CY7C0241AV/0251AV/036AV
Document #: 38-06052 Rev. *E
Page 5 of 19
Architecture
The CY7C024AV/025AV/026AV and CY7C0241AV/0251AV/
036AV consist of an array of 4K, 8K, and 16K words of 16 and
18 bits each of dual-port RAM cells, I/O and address lines, and
control signals (CE, OE, R/W). These control pins permit
independent access for reads or writes to any location in
memory. To handle simultaneous writes/reads to the same
location, a BUSY pin is provided on each port. Two Interrupt
(INT) pins can be utilized for port-to-port communication. Two
Semaphore (SEM) control pins are used for allocating shared
resources. With the M/S pin, the devices can function as a
master (BUSY pins are outputs) or as a slave (BUSY pins are
inputs). The devices also have an automatic power-down
feature controlled by CE. Each port is provided with its own
output enable control (OE), which allows data to be read from
the device.
Functional Description
The CY7C024AV/025AV/026AV and CY7C0241AV/0251AV
/036AV are low-power CMOS 4K, 8K, and 16K ×16/18
dual-port static RAMs. Various arbitration schemes are
included on the devices to handle situations when multiple
processors access the same piece of data. Two ports are
provided, permitting independent, asynchronous access for
reads and writes to any location in memory. The devices can
be utilized as standalone 16/18-bit dual-port static RAMs or
multiple devices can be combined in order to function as a
32/36-bit or wider master/slave dual-port static RAM. An M/S
pin is provided for implementing 32/36-bit or wider memory
applications without the need for separate master and slave
devices or additional discrete logic. Application areas include
interprocessor/multiprocessor
designs,
communications
status buffering, and dual-port video/graphics memory.
Each port has independent control pins: Chip Enable (CE),
Read or Write Enable (R/W), and Output Enable (OE). Two
flags are provided on each port (BUSY and INT). BUSY
signals that the port is trying to access the same location
currently being accessed by the other port. The Interrupt flag
(INT) permits communication between ports or systems by
means of a mail box. The semaphores are used to pass a flag,
or token, from one port to the other to indicate that a shared
resource is in use. The semaphore logic is comprised of eight
shared latches. Only one side can control the latch
(semaphore) at any time. Control of a semaphore indicates
that a shared resource is in use. An automatic power-down
feature is controlled independently on each port by a Chip
Select (CE) pin.
The CY7C024AV/025AV/026AV and CY7C0241AV/0251AV/
036AV are available in 100-pin Thin Quad Plastic Flatpacks
(TQFP).
Write Operation
Data must be set up for a duration of tSD before the rising edge
of R/W in order to guarantee a valid write. A write operation is
controlled by either the R/W pin (see Write Cycle No. 1
waveform) or the CE pin (see Write Cycle No. 2 waveform).
Required inputs for non-contention operations are summarized
in Table 1.
If a location is being written to by one port and the opposite
port attempts to read that location, a port-to-port flowthrough
delay must occur before the data is read on the output;
otherwise the data read is not deterministic. Data will be valid
on the port tDDD after the data is presented on the other port.
Read Operation
When reading the device, the user must assert both the OE
and CE pins. Data will be available tACE after CE or tDOE after
OE is asserted. If the user wishes to access a semaphore flag,
then the SEM pin must be asserted instead of the CE pin, and
OE must also be asserted.
Pin Definitions
Left Port
Right Port
Description
CEL
CER
Chip Enable.
R/WL
R/WR
Read/Write Enable.
OEL
OER
Output Enable.
A0L–A13L
A0R–A13R
Address (A0–A11 for 4K devices; A0–A12 for 8K devices; A0–A13 for
16K).
I/O0L–I/O17L
I/O0R–I/O17R
Data Bus Input/Output.
SEML
SEMR
Semaphore Enable.
UBL
UBR
Upper Byte Select (I/O8–I/O15 for x16 devices; I/O9–I/O17 for x18
devices).
LBL
LBR
Lower Byte Select (I/O0–I/O7 for x16 devices; I/O0–I/O8 for x18
devices).
INTL
INTR
Interrupt Flag.
BUSYL
BUSYR
Busy Flag.
M/S
Master or Slave Select.
VCC
Power.
GND
Ground.
NC
No Connect.
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