Document Number: 38-06046 Rev. *J Page 6 of 24
Architecture
The CY7C026A consists of an array of 16K words of 16 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 Overview
Write Operation
Data must be set up for a duration of t
SD
before the rising edge
of R/W
to either the R/W pin (see Figure 6 on page 15) or the CE
pin (see Figure 7 on page 15). 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 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 wishes to access a semaphore flag, then the
SEM
pin must be asserted instead of the CE pin, and OE must
also be asserted.
Table 1. Non-Contending Read/Write
Inputs Outputs
Operation
CE R/W OE UB LB SEM I/O
8
–I/O
15
I/O
0
–I/O
7
H X X X X H High Z High Z Deselected: Power-down
X X X H H H High Z High Z Deselected: Power-down
L L X L H H Data in High Z Write to upper byte only
L L X H L H High Z Data in Write to lower byte only
L L X L L H Data in Data in Write to both bytes
L H L L H H Data out High Z Read upper byte only
L H L H L H High Z Data out Read lower byte only
L H L L L H Data out Data out Read both bytes
X X H X X X High Z High Z Outputs disabled
H H L X X L Data out Data out Read data in semaphore flag
H H L H H L Data out Data out Read data in semaphore flag
H X X X L Data in Data in Write D
IN0
into semaphore flag
H X H H L Data in Data in Write D
IN0
into semaphore flag
L X X L X L Not allowed
L X X X L L Not allowed
