Cypress CY7C0251AV - Manual (Page 5)

CY7C024AV/024BV/025AV/026AV
CY7C0241AV/0251AV/036AV
Document #: 38-06052 Rev. *J Page 5 of 19
Architecture
The CY7C024AV/024BV/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, IO and
address lines, and control signals (CE, OE, RW). These control pins
permit independent access for reads or writes to any location in
memory. To handle simultaneous writes and reads to the same
location, a BUSY pin is provided on each port. Two Interrupt (INT)
pins can be used 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). They also have an
automatic power down feature controlled by CE. Each port has its
own output enable control (OE), which enables data to be read from
the device.
Functional Description
The CY7C024AV/024BV/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. There are two ports
permitting independent, asynchronous access for reads and writes
to any location in memory. The devices can be used as standalone
16 or18-bit dual port static RAMs or multiple devices can be
combined to function as a 32 or 36-bit or wider master and slave
dual port static RAM. An M/S pin is provided for implementing 32 or
36-bit or wider memory applications. It does not need separate
master and slave devices or additional discrete logic. Application
areas include interprocessor/multiprocessor designs, communica-
tions status buffering, and dual port video and 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 has 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/024BV/025AV/026AV and
CY7C0241AV0251AV/036AV are available in 100-pin Pb-free Thin
Quad Flat Pack (TQFP) and 100-pin TQFP.
Write Operation
Data must be set up for a duration of t
SD
before the rising edge
of RW to guarantee a valid write. A write operation is controlled
by either the RW pin (see
Figure 8 on page 12) or the CE pin (see
Figure 9 on page 12). Required inputs for non-contention opera-
tions are summarized in Table 1 on page 7.
If a location is being written to by one port and the opposite port
tries to read that location, there must be a port to port flowthrough
delay before the data is read on the output; otherwise the data
read is not deterministic. Data is valid on the port t
DDD
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 is available t
ACE
after CE or t
DOE
after OE is
asserted. If the user wants to access a semaphore flag, then the
SEM pin and OE must be asserted.
Interrupts
The upper two memory locations are for message passing. The
highest memory location (FFF for the
CY7C024AV/024BV/41AV/1FFF for the CY7C025AV/51AV,
Pin Definitions
Left Port Right Port Description
CE
L
CE
R
Chip Enable
R/W
L
R/W
R
Read and Write Enable
OE
L
OE
R
Output Enable
A
0L
–A
13L
A
0R
–A
13R
Address (A
0
–A
11
for 4K devices; A
0
–A
12
for 8K devices; A
0
–A
13
for 16K)
IO
0L
–IO
17L
IO
0R
–IO
17R
Data Bus Input and Output
SEM
L
SEM
R
Semaphore Enable
UB
L
UB
R
Upper Byte Select (IO
8
–IO
15
for x16 devices; IO
9
–IO
17
for x18 devices)
LB
L
LB
R
Lower Byte Select (IO
0
–IO
7
for x16 devices; IO
0
–IO
8
for x18 devices)
INT
L
INT
R
Interrupt Flag
BUSY
L
BUSY
R
Busy Flag
M/S Master or Slave Select
V
CC
Power
GND Ground
NC No Connect
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