MA7001 Datasheet, PDF (6/15 Pages) Dynex Semiconductor – Radiation Hard 512x9 Bit FIFO

MA7001
SIGNAL DESCRIPTIONS
Reset (RS)
Reset occurs when RS is in a low state, setting both read and
write pointers to the first location in memory. Reset is required
prior to the first write. Both READ (R) and WRITE (W) signals
must be in high states during reset.
Read Enable (R):
Providing the EMPTY FLAG (EF) is not set, i.e. there is still
data to be read, a read cycle commences on the falling edge of
R, (see Figure 16). Data is read in a First-ln First-Out manner
independent of write operations. When reads are disabled
data outputs (Q0 - Q8) are in a high impedance state. Reading
the last available memory location sets the EMPTY FLAG
(EF), which is cleared following a write cycle.
As a WRITE operation is being performed to the last physical
memory location (511th) whilst the READ pointer is waiting at
the 510th physical location the FULL flag is activated for a
duration less than 20ns.
Note: The last physical location (511th) is accessed after 511
WRITE or READ operations after RESET.
Empty Flag (EF):
Following an initial RESET EF is active, becoming inactive
after the first write cycle, (see Figure 20). EF becomes active
once the read and write pointers are coincident following a
read cycle. Reading will not take place whilst EF is active, and
may only proceed once a write cycle has occured.
Write Enable (W):
Providing the FULL FLAG (FF) is not set, i.e. there exists at
least one memory location for writing, a write cycle
commences on the falling edge of (W), (see Figure 17). Data is
written into consecutive memory locations independent of read
operations on the rising edge of W. Data set up and hold times
are with respect to the rising edge of W.
Expansion In (Xl):
There are two possible modes of operation for the FIFO. One
with Xl grounded in which the device is in singledevice mode,
the other is a depth expension mode or daisy chain
configuration. In the latter mode Xl inputs come from
EXPANSION OUT (XO) outputs of the device preceding it in
the chain.
Expansion Out (XO):
In depth expansion mode XO from one device signals the next
device in the chain that the last location in its memory has been
accessed.
Full Flag (FF):
FF becomes active when the last available memory location
has been written to, (see Figure 18). In general, this occurs
whenever the write pointer coincides with the read pointer
following a write cycle. Writes are inhibited while FF is active,
and may only proceed after a read cycle has occured.
FF will go high t_RFF after completion of a valid READ operation.
FF will go low t_WFF from the beginning of a subsequent WRITE
operation, provided that a second READ has not been
completed. Writes beginning t_FFW after FF goes high, are valid.
Writes beginning after FF goes low and ending more than t_WPI
before FF goes high, are invalid (ignored). Writes beginning
less than twpl before FF goes high and less than t_FFW later,
may or may not occur (be valid) depending on the internal flag
status (see Figure 19).
EF will go high t_WEF after completion of a valid WRITE
operation. EF will again go low t_REF from the beginning of a
subsequent READ operation, provided that a second WRITE
has not been completed. Reads beginning t_EFR after EF goes
high, are valid. Reads begun after EF goes low and ending
more than t_RPI before EF goes high, are invalid (ignored).
Reads beginning less than t_RIP before EF goes high and less
than t_EFR later, may or may not occur (be valid) depending on
the internal flag status (See Figure 21). If a Read to the last but
one physical location completes while the last location (511th)
is being written, the EF will not be activated. The next Read
should be activated after the last Write has completed.
First Load/Retransmit (FL/RT):
This is a dual purpose input depending on the mode of
operation of the device. In single device mode Xl = 0 data may
be retransmitted, i.e. it may be re-read. In depth expansion
mode FL signifies the first device in the chain. When RT is
pulsed low the read pointer is set to the first memory location.
The write pointer is unaffected. This feature is disabled in
depth expansion mode, and can only be applied when R and
W are inactive (See Figure 22).
Data Inputs (D0 - D8): Data inputs, 9 bit word, for write
operations.
Data Outputs (Q0 - Q8):
Data outputs, 9 bit word, for read operations. When R is
inactive these outputs are in a high impedance state.
If a Write to the last but one physical location completes while
the last location (511th) is being Read, the FF will not be
activated. The next Read should start after the last Write has
completed.
6/15