1CY 7C40 2
CY7C401/CY7C403
CY7C402/CY7C404
64 x 4 Cascadable FIFO
64 x 5 Cascadable FIFO
Features
• 64 x 4 (CY7C401 and CY7C403)
64 x 5 (CY7C402 and CY7C404)
High-speed first-in first-out memory (FIFO)
• Processed with high-speed CMOS for optimum
speed/power
• 25-MHz data rates
• 50-ns bubble-through time—25 MHz
• Expandable in word width and/or length
• 5-volt power supply
±
10% tolerance, both commercial
and military
• Independent asynchronous inputs and outputs
• TTL-compatible interface
• Output enable function available on CY7C403 and
CY7C404
• Capable of withstanding greater than 2001V electro-
static discharge
• Pin compatible with MMI 67401A/67402A
words. Both the CY7C403 and CY7C404 have an output en-
able (OE) function.
The devices accept 4- or 5-bit words at the data input (DI
0
–
DI
n
) under the control of the shift in (SI) input. The stored
words stack up at the output (DO
0
– DO
n
) in the order they
were entered. A read command on the shift out (SO) input
causes the next to last word to move to the output and all data
shifts down once in the stack. The input ready (IR) signal acts
as a flag to indicate when the input is ready to accept new data
(HIGH), to indicate when the FIFO is full (LOW), and to provide
a signal for a cascading. The output ready (OR) signal is a flag
to indicate the output contains valid data (HIGH), to indicate
the FIFO is empty (LOW), and to provide a signal for cascad-
ing.
Parallel expansion for wider words is accomplished by logical-
ly ANDing the IR and OR signals to form composite signals.
Serial expansion is accomplished by tying the data inputs of
one device to the data outputs of the previous device. The IR
pin of the receiving device is connected to the SO pin of the
sending device, and the OR pin of the sending device is con-
nected to the SI pin of the receiving device.
Reading and writing operations are completely asynchronous,
allowing the FIFO to be used as a buffer between two digital
machines of widely differing operating frequencies. The
25-MHz operation makes these FIFOs ideal for high-speed
communication and controller applications.
Functional Description
The CY7C401 and CY7C403 are asynchronous first-in
first-out (FIFOs) organized as 64 four-bit words. The CY7C402
and CY7C404 are similar FIFOs organized as 64 five-bit
Logic Block Diagram
SI
IR
INPUT
CONTROL
LOGIC
Pin Configurations
DIP
WRITE POINTER
(CY7C401) NC
(CY7C403) OE
IR
SI
DI
0
DI
1
DI
2
DI
3
GND
1
16
2
15
3
14
4 CY7C401
13
CY7C403
5
12
6
11
10
7
9
8
VCC
SO
OR
DO
0
DO
1
DO
2
DO
3
MR
(CY7C402) NC
(CY7C404) OE
IR
SI
DI
0
DI
1
DI
2
DI
3
DI
4
GND
DIP
1
18
2
17
3
16
4 CY7C402
15
CY7C404
5
14
6
13
12
7
11
8
10
9
VCC
SO
OR
DO
0
DO
1
DO
2
DO
3
DO
4
MR
WRITE MULTIPLEXER
DI 0
DI 1
DI 2
DI 3
(DI 4)
DATAIN
MEMORY
ARRAY
OUTPUT
ENABLE
OE
DO0
DO1
DATA
IN
DO2
DO3
(DO 4)
C401–2
C401–4
LCC
LCC
MR
MASTER
RESET
READ MULTIPLEXER
OUTPUT
CONTROL
LOGIC
SO
OR
C401–1
SI
DI
0
DI
1
DI
2
NC
READ POINTER
3 2 1 2019
4
18 NC
5
17 OR
CY7C401
6 CY7C403 16 DO
0
7
15 DO
1
8
14 DO
2
910111213
SI
DI
0
DI
1
DI
2
DI
3
3 2 1 2019
4
18 OR
5
17 DO
0
6 CY7C402 16 DO
1
7 CY7C404 15 DO
2
8
14 DO
3
910111213
C401–3
C401–5
Selection Guide
7C401/2–5
Operating Frequency (MHz)
Maximum Operating
Current (mA)
Commercial
Military
5
75
7C40X–10
10
75
90
7C40X–15
15
75
90
7C40X–25
25
75
90
Cypress Semiconductor Corporation
•
3901 North First Street
•
San Jose
•
CA 95134 •
408-943-2600
March 1986 – Revised April 1995
CY7C401/CY7C403
CY7C402/CY7C404
Maximum Ratings
(Above which the useful life may be impaired. For user guide-
lines, not tested.)
Storage Temperature ................................. –65°C to +150°C
Ambient Temperature with
Power Applied............................................. –55°C to +125°C
Supply Voltage to Ground Potential ............... –0.5V to +7.0V
DC Voltage Applied to Outputs
in High Z State ............................................... –0.5V to +7.0V
DC Input Voltage............................................ –3.0V to +7.0V
Power Dissipation ..........................................................1.0W
Output Current, into Outputs (LOW)............................ 20 mA
Static Discharge Voltage ........................................... >2001V
(per MIL-STD-883, Method 3015)
Latch-Up Current ..................................................... >200 mA
Operating Range
Range
Commercial
Military
[1]
Ambient
Temperature
0
°
C to +70
°
C
–55
°
C to +125
°
C
V
CC
5V
±10%
5V
±10%
Electrical Characteristics
Over the Operating Range (Unless Otherwise Noted)
[2]
7C40X–10, 15, 25
Parameter
V
OH
V
OL
V
IH
V
IL
I
IX
V
CD[3]
I
OZ
I
OS
I
CC
Description
Output HIGH Voltage
Output LOW Voltage
Input HIGH Voltage
Input LOW Voltage
Input Leakage Current
Input Diode Clamp Voltage
[3]
Output Leakage Current
Output Short Circuit Current
[4]
Power Supply Current
GND
≤
V
OUT
≤
V
CC
, V
CC
= 5.5V
Output Disabled (CY7C403 and CY7C404)
V
CC
= Max., V
OUT
= GND
V
CC
= Max., I
OUT
= 0 mA
Commercial
Military
–50
+50
–90
75
90
µA
mA
mA
mA
GND
≤
V
I
≤
V
CC
Test Conditions
V
CC
= Min., I
OH
= –4.0 mA
V
CC
= Min., I
OL
= 8.0 mA
2.0
–3.0
–10
Min.
2.4
0.4
6.0
0.8
+10
Max.
Unit
V
V
V
V
µA
Capacitance
[5]
Parameter
C
IN
C
OUT
Description
Input Capacitance
Output Capacitance
Test Conditions
T
A
= 25°C, f = 1 MHz,
V
CC
= 4.5V
Max.
5
7
Unit
pF
pF
Notes:
1. T
A
is the “instant on” case temperature.
2. See the last page of this specification for Group A subgroup testing information.
3. The CMOS process does not provide a clamp diode. However, the FIFO is insensitive to –3V dc input levels and –5V undershoot pulses of less than 10 ns
(measured at 50% output).
4. For test purposes, not more than one output at a time should be shorted. Short circuit test duration should not exceed 30 seconds.
5. Tested initially and after any design or process changes that may affect these parameters.
2
CY7C401/CY7C403
CY7C402/CY7C404
Operational Description
Concept
Unlike traditional FIFOs, these devices are designed using a
dual-port memory, read and write pointer, and control logic.
The read and write pointers are incremented by the SO and SI
respectively. The availability of an empty space to shift in data
is indicated by the IR signal, while the presence of data at the
output is indicated by the OR signal. The conventional concept
of bubble-through is absent. Instead, the delay for input data
to appear at the output is the time required to move a pointer
and propagate an OR signal. The output enable (OE) signal
provides the capability to OR tie multiple FIFOs together on
a common bus.
Resetting the FIFO
Upon power-up, the FIFO must be reset with a master reset
(MR) signal. This causes the FIFO to enter an empty condition
signified by the OR signal being LOW at the same time the IR
signal is HIGH. In this condition, the data outputs (DO
0
– DO
n
)
will be in a LOW state.
Shifting Data In
Data is shifted in on the rising edge of the SI signal. This loads
input data into the first word location of the FIFO. On the falling
edge of the SI signal, the write pointer is moved to the next
word position and the IR signal goes HIGH, indicating the
readiness to accept new data. If the FIFO is full, the IR will
remain LOW until a word of data is shifted out.
Shifting Data Out
Data is shifted out of the FIFO on the falling edge of the SO
signal. This causes the internal read pointer to be advanced to
the next word location. If data is present, valid data will appear
on the outputs and the OR signal will go HIGH. If data is not
present, the OR signal will stay LOW indicating the FIFO is
empty. Upon the rising edge of SO, the OR signal goes LOW.
The data outputs of the FIFO should be sampled with
edge-sensitive type D flip-flops (or equivalent), using the SO
signal as the clock input to the flip-flop.
Bubble-Through
Two bubble-through conditions exist. The first is when the de-
vice is empty. After a word is shifted into an empty device, the
data propagates to the output. After a delay, the OR flag goes
HIGH, indicating valid data at the output.
The second bubble-through condition occurs when the device
is full. Shifting data out creates an empty location that propa-
gates to the input. After a delay, the IR flag goes HIGH. If the
SI signal is HIGH at this time, data on the input will be shifted
in.
Possible Minimum Pulse Width Violation at the Boundary
Conditions
If the handshaking signals IR and OR are not properly used to
generate the SI and SO signals, it is possible to violate the
minimum (effective) SI and SO positive pulse widths at the full
and empty boundaries.
When this violation occurs, the operation of the FIFO is unpre-
dictable. It must then be reset, and all data is lost.
Application of the 7C403–25/7C404–25 at 25 MHz
Application of the CY7C403 or CY7C404 Cypress CMOS
FIFOs requires knowledge of characteristics that are not easily
specified in a datasheet, but which are necessary for reliable
operation under all conditions, so we will specify them here.
When an empty FIFO is filled with initial information at maxi-
mum “shift in” SI frequency, followed by immediate shifting out
of the data also at maximum “shift out” SO frequency, the de-
signer must be aware of a window of time which follows the
initial rising edge of the OR signal, during which time the SO
signal is not recognized. This condition exists only at
high-speed operation where more than one SO may be gen-
erated inside the prohibited window. This condition does not
inhibit the operation of the FIFO at full-frequency operation,
but rather delays the full 25-MHz operation until after the win-
dow has passed.
There are several implementation techniques for managing
the window so that all SO signals are recognized:
1. The first involves delaying SO operation such that it does
not occur in the critical window. This can be accomplished
by causing a fixed delay of 40 ns “initiated by the SI signal
only when the FIFO is empty” to inhibit or gate the SO ac-
tivity. However, this requires that the SO operation be at
least temporarily synchronized with the input SI operation.
In synchronous applications this may well be possible and
a valid solution.
2. Another solution not uncommon in synchronous applica-
tions is to only begin shifting data out of the FIFO when it is
more than half full. This is a common method of FIFO ap-
plication, as earlier FIFOs could not be operated at maxi-
mum frequency when near full or empty. Although Cypress
FIFOs do not have this limitation, any system designed in
this manner will not encounter the window condition de-
scribed above.
3. The window may also be managed by not allowing the first
SO signal to occur until the window in question has passed.
This can be accomplished by delaying the SO 40 ns from
the rising edge of the initial OR signal. This however in-
volves the requirement that this only occurs on the first oc-
currence of data being loaded into the FIFO from an empty
condition and therefore requires the knowledge of IR and
SI conditions as well as SO.
4. Handshaking with the OR signal is a third method of avoid-
ing the window in question. With this technique the rising
edge of SO, or the fact that SO signal is HIGH, will cause
the OR signal to go LOW. The SO signal is not taken LOW
again, advancing the internal pointer to the next data, until
the OR signal goes LOW. This ensures that the SO pulse
that is initiated in the window will be automatically extended
long enough to be recognized.
5. There remains the decision as to what signal will be used
to latch the data from the output of the FIFO into the receiv-
ing source. The leading edge of the SO signal is most ap-
propriate because data is guaranteed to be stable prior to
and after the SO leading edge for each FIFO. This is a
solution for any number of FIFOs in parallel.
Any of the above solutions will ensure the correct operation of
a Cypress FIFO at 25 MHz. The specific implementation is left
to the designer and is dependent on the specific application
needs.
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