M67204E
4 K
9 CMOS Parallel FIFO Rad Tolerant
Introduction
The M67204E implement a first-in first-out algorithm,
featuring asynchronous read/write operations. The FULL
and EMPTY flags prevent data overflow and underflow.
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 Wireless & Microcontrollers
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
resets 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 eigh transistors (8 T) memory cell, the
M67204E combine an extremely low standby supply
current (typ = 1.0
µA)
with a fast access time at 40 ns
over the full temperature range. All versions offer battery
backup data retention capability with a typical power
consumption at less than 2
µW.
The M67204E is processed according to the methods of
the latest revision of the MIL STD 883 (class B or S), ESA
SCC 9000 and QML.
Features
D
D
D
D
First-in first-out dual port memory
4096
×
9 organisation
Fast access time: 40, 50 ns
Wide temperature range : – 55
°C
to + 125
°C
D
D
D
D
D
D
D
D
D
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 2 V data retention
TTL compatible
Single 5 V
±
10 % power supply
High performance SCMOS technology
Rev. G – June 5, 2000
1
M67204E
Interface
Block Diagram
Pin Configuration
DIL ceramic 28 pin 300 mils
FP 28 pin 400 mils
(top view)
W
I
8
I
3
I
2
I
1
I
0
XI
FF
Q
0
Q
1
Q
2
Q
3
Q
8
GND
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
V
CC
I
4
I
5
I
6
I
7
FL/RT
RS
EF
XO/HF
Q
7
Q
6
Q
5
Q
4
R
2
Rev. G – June 5, 2000
M67204E
Pin Names
NAMES
I0–8
Q0–8
W
R
RS
EF
Inputs
Outputs
Write Enable
Read Enable
Reset
Empty Flag
DESCRIPTION
NAMES
FF
XO/HF
XI
FL/RT
VCC
GND
DESCRIPTION
Full Flag
Expansion Out/Half-Full Flag
Expansion IN
First Load/Retransmit
Power Supply
Ground
Signal Description
Data In (I0 - I8)
Data inputs for 9-bit data
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).
Reset (RS)
Reset occurs whenever the Reset (RS) input is taken to a
low state. Reset returns both internal read and write
Figure 1. Reset.
Notes :
1. EF, FF and HF may change status during reset, but flags will be valid at t
RSC
.
2. W and R = V
IH
around the rising edge of RS.
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 of 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
Rev. G – June 5, 2000
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 operations. 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.
3
M67204E
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 Outputs (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.
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.
Full Flag (FF)
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.
Empty Flag (EF)
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.
First Load/Retransmit (FL/RT)
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 connecting the
Expansion In (XI) to ground.
The M67204E 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 location 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 have 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.
Expansion Out/Half-full Flag (XO/HF)
This is a dual-purpose output. In the single device mode,
when Expansion In (XI) is connected 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.
4
Rev. G – June 5, 2000
M67204E
Functional Description
Operating Modes
Single Device Mode
A single M67204E may be used when the application
requirements are for 4096 words or less. The M67204E is
Figure 2. Block Diagram of Single 4K
×
9 FIFO.
HF
(HALF–FULL FLAG)
WRITE
(W)
9
DATA
IN
(I)
(R)
9
READ
in a Single Device Configuration when the Expansion In
(XI) control input is grounded (see Figure 2). In this mode
the Half-Full Flag (HF), which is an active low output, is
shared with Expansion Out (XO).
M
67204E
(Q)
DATA
OUT
FULL FLAG (FF)
RESET
(RS)
(EF) EMPTY FLAG
(RT) RETRANSMIT
EXPANSION IN (XI)
Width Expansion Mode
Word width may be increased simply by connecting the
corresponding input control signals of multiple devices.
Status flags (EF, FF and HF) can be detected from any
device. Figure 3 demonstrates an 18-bit word width by
using two M67204E. Any word width can be attained by
adding additional M67204E.
Figure 3. Block Diagram of 4096
×
18 FIFO Memory Used in Width Expansion Mode.
HF
9
DATA
IN
(I)
(R) READ
WRITE
FULL FLAG
RESET
(RS)
9
(W)
(FF)
HF
9
18
M
67204E
M
67204E
(EF) EMPTY FLAG
(RT) RETRANSMIT
9
XI
XI
18
(Q) DATA
OUT
Note :
3. Flag detection is accomplished by monitoring the FF, EF and the HF signals on either (any) device used in the width
expansion configuration. Do not connect any output control signals together.
Rev. G – June 5, 2000
5
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