Features
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First-in first-out dual port memory
4096 y 9 organisation
Fast Flag and access times: 15, 30 ns
Wide temperature range: - 55°C to + 125°C
Fully expandable by word width or depth
Asynchronous read/write operations
Empty, full and half flags in single device mode
Retransmit capability
Bi-directional applications
Battery back-up operation: 2V data retention
TTL compatible
Single 5V + 10% power supply
QML Q and V with SMD 5962-89568
Description
The M67204F implements a first-in first-out algorithm, featuring asynchronous
read/write operations. The FULL and EMPTY flags prevent data overflow and under-
flow. The Expansion logic allows unlimited expansion in word size and depth with no
timing penalties. Twin address pointers automatically generate internal read and write
addresses, and no external address information are required for the Atmel FIFOs.
Address pointers are automatically incremented with the write pin and read pin. The 9
bits wide data are used in data communications applications where a parity bit for
error checking is necessary. The Retransmit pin reset the Read pointer to zero without
affecting the write pointer. This is very useful for retransmitting data when an error is
detected in the system.
Using an array of eight transistors (8 T) memory cell, the M67204F combine an
extremely low standby supply current (typ = 0.1
µA)
with a fast access time at 15 ns
over the full temperature range. All versions offer battery backup data retention capa-
bility with a typical power consumption at less than 2
µW.
The M67204F is processed according to the methods of the latest revision of the MIL
PRF 38535 (Q and V) or ESA SCC 9000.
Rad Tolerant
High Speed
4Kx9
Parallel FIFO
M67204F
Rev. E–20-Aug-01
1
Pin Names
NAMES
FF
XO/HF
XI
FL/RT
VCC
GND
I0-8
Q0-8
W
R
RS
EF
Full Flag
Expansion Out/Half-Full Flag
Expansion IN
First Load/Retransmit
Power Supply
Ground
Inputs
Outputs
Write Enable
Read Enable
Reset
Empty Flag
DESCRIPTION
Signal Description
Data In (I
0
- I
8
)
Reset (RS)
Data inputs for 9 - bit data
Reset occurs whenever the Reset (RS) input is taken to a low state. Reset returns both
internal read and write pointers to the first location. A reset is required after power-up
before a write operation can be enabled. Both the Read Enable (R) and Write Enable
(W) inputs must be in the high state during the period shown in Figure 1 (i.e. t
RSS
before
the rising edge of RS) and should not change until t
RSR
after the rising edge of RS. The
Half-Full Flag (HF) will be reset to high After Reset (RS).
Figure 1.
Reset
1. EF, FF and HF may change status during reset, but flags will be valid at t
RSC
.
2. W and R = VIH around the rising edge of RS.
3
M67204F
Rev. E–20-Aug-01
M67204F
Write Enable (W)
A write cycle is initiated on the falling edge of this input if the Full Flag (FF) is not set.
Data set-up and hold times must be maintained in the rise time of the leading edge of
the Write Enable (W). Data is stored sequentially in the Ram array, regardless of any
current read operation.
Once half the memory is filled, and during the falling edge of the next write operation,
the Half-Full Flag (HF) will be set to low and remain in this state until the difference
between the write and read pointers is less than or equal to half of the total available
memory in the device. The Half-Full Flag (HF) is then reset by the rising edge of the
read operation.
To prevent data overflow, the Full Flag (FF) will go low, inhibiting further write opera-
tions. On completion of a valid read operation, the Full Flag (FF) will go high after TRFF,
allowing a valid write to begin. When the FIFO stack is full, the internal write pointer is
blocked from W, so that external changes to W will have no effect on the full FIFO stack.
Read Enable (R)
A read cycle is initiated on the falling edge of the Read Enable (R) provided that the
Empty Flag (EF) is not set. The data is accessed on a first in/first out basis, not with
standing any current write operations. After Read Enable (R) goes high, the Data Out-
puts (Q0 - Q8) will return to a high impedance state until the next Read operation. When
all the data in the FIFO stack has been read, the Empty Flag (EF) will go low, allowing
the “final” read cycle, but inhibiting further read operations whilst the data outputs
remain in a high impedance state. Once a valid write operation has been completed, the
Empty Flag (EF) will go high after tWEF and a valid read may then be initiated. When
the FIFO stack is empty, the internal read pointer is blocked from R, so that external
changes to R will have no effect on the empty FIFO stack.
This is a dual-purpose input. In the Depth Expansion Mode, this pin is connected to
ground to indicate that it is the first loaded (see Operating Modes). In the Single Device
Mode, this pin acts as the retransmit input. The Single Device Mode is initiated by con-
necting the Expansion In (XI) to ground.
The M67204F can be made to retransmit data when the Retransmit Enable Control (RT)
input is pulsed low. A retransmit operation will set the internal read point to the first loca-
tion and will not affect the write pointer. Read Enable (R) and Write Enable (W) must be
in the high state during retransmit. The retransmit feature is intended for use when a
number of writes equals to or less than the depth of the FIFO has occured since the last
RS cycle. The retransmit feature is not compatible with the Depth Expansion Mode and
will affect the Half-Full Flag (HF), in accordance with the relative locations of the read
and write pointers.
First Load/Retransmit
(FL/RT)
Expansion In (XI)
This input is a dual-purpose pin. Expansion In (XI) is connected to GND to indicate an
operation in the single device mode. Expansion In (XI) is connected to Expansion Out
(XO) of the previous device in the Depth Expansion or Daisy Chain modes.
The Full Flag (FF) will go low, inhibiting further write operations when the write pointer is
one location less than the read pointer, indicating that the device is full. If the read
pointer is not moved after Reset (RS), the Full Flag (FF) will go low after 4096 writes.
The Empty Flag (EF) will go low, inhibiting further read operations when the read pointer
is equal to the write pointer, indicating that the device is empty.
Full Flag (FF)
Empty Flag (EF)
4
Rev. E–20-Aug-01
Expansion Out/Half-Full
Flag (XO/HF)
This is a dual-purpose output. In the single device mode, when Expansion In (XI) is con-
nected to ground, this output acts as an indication of a half-full memory.
After half the memory is filled and on the falling edge of the next write operation, the
Half-Full Flag (HF) will be set to low and will remain set until the difference between the
write and read pointers is less than or equal to half of the total memory of the device.
The Half-Full Flag (HF) is then reset by the rising edge of the read operation.
In the Depth Expansion Mode, Expansion In (XI) is connected to Expansion Out (XO) of
the previous device. This output acts as a signal to the next device in the Daisy Chain by
providing a pulse to the next device when the previous device reaches the last memory
location.
Data Output (Q
0
- Q
8
)
DATA output for 9-bit wide data. This data is in a high impedance condition whenever
Read (R) is in a high state.
5
M67204F
Rev. E–20-Aug-01
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