When using the DLX1414 on a separate display board with
more than 6 inches of cable length, it may be necessary to
buffer all inputs. This is most easily achieved with Hex
non-inverting buffers such as the 74365. The object is to
prevent transient current in the protection diodes. The
buffers should be located on the display board near the dis-
plays.
Figure 5. Data loading table
Address
WR A1 A0 D6 D5 D4 D3 D2 D1 D0
Digit
3
Digit
2
Digit
1
Digit
0
Data Input
NC
A
NC
NC
B
H
L
L
X
L
L
X
L
X
X
L
L
X
L
L
X
L
L
X
L
L
X
L
X
H
L
NC
NC
NC
NC
NC
H
H
L
A
H
H
L
L
L
L
L
Local power supply bypass capacitors are also needed in
many cases. These should be 6 or 10 volt, tantalum type
with 10 µF or greater capacitance. Low internal resistance
is important due to current steps which result from the
internal multiplexing of the displays.
H
H
L
L
H
L
L
–
H
H
H
H
–
L
L
L
L
–
L
L
L
L
–
L
L
L
H
–
L
H
H
L
–
H
L
L
H
–
H
L
NC
D
C
C
C
K
B
B
B
B
A
A
E
E
H
H
–
D
H
–
D
See Character Set
NC=No change
If small wire cables are used, good engineering practice is
to calculate the wire resistance of the ground plus the +5
volt wires. More than 0.1 volt drop, (at 25 mA per digit
worst case) should be avoided, since this loss is in addition
to any inaccuracies or load regulation limitations of the
power supply.
X=Don't care
Figure 6. General interface circuit
Vcc
GND
The 5-volt power supply for the displays should be the
Display
D15 D12 D11
Display
Display
Display
D0
same one supplying V to all logic devices which drive
D0–A6
D8 D7 D4 D3
CC
2
the display devices. If a separate supply must be used,
then local buffers using hex, non-inverting gates should be
used on all inputs and these buffers should be powered
from the display power supply. This precaution is to avoid
/
WR
WR
WR
WR
A0
A1
Digit
Select
WR
A3
A2
D
C
B
A
logic inputs higher than display V during power up or
CC
Decoder
line transients.
Interfacing the DLX1414
A general and straightforward interface circuit is shown in
Figure 6. This scheme can easily interface to LP systems
or any other systems which can provide the seven data
lines, appropriate address and control lines.
Figure 7. Gating the write pulse
0
1
7a.
2
The DLX1414 does not have a chip enable input; therefore
each display in a system requires its Write pulse be gated
with appropriate address signals. Figure 7a shows the use
of a 74154 decoder (4 lines to 16 lines) for up to a 64 char-
acter display. Using the G1 input for display select (address
select in a memory mapped system) and the G2 input to
gate the Write signal. Another approach (Figure 7b and 7c)
which minimizes logic for a 16 or 32 digit display takes
advantage of decoding scheme of the 7442 decoder.
Display Select
G
G
A
B
C
D
1
2
3
4
WR
A2
A3
A4
A5
5
6
74154
to WR
of Display
7
8
9
10
11
12
13
14
15
Parallel l/O
9
8
7
6
5
4
3
2
1
0
7b.
Digit Select
D
C
B
A
The parallel l/O device of a microprocessor can be con-
nected easily to the circuit in Figure 6. One eight bit output
port can provide the seven input data bits. Another eight
bit output port can contain the address and control signals.
Unused
to WR
WR
A3
A2
7442
of Display
9
7c.
Unused
8
7
6
5
4
3
2
1
0
Digit Select
D
C
B
A
WR
A4
7442
to WR
of Display
A3
A2
2000 Infineon Technologies Corp. • Optoelectronics Division • San Jose, CA
www.infineon.com/opto • 1-888-Infineon (1-888-463-4636)
OSRAM Opto Semiconductors GmbH & Co. OHG • Regensburg, Germany
www.osram-os.com • +49-941-202-7178
Appnote 15
3
May 31, 2000-12
OSRAM [ OSRAM GMBH ]
