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Lecture 7. Digital Display
Binary numbers are necessary, but very hard to read or interpret.
What is available to display binary to decimal information?
A seven-segment L.E.D. display.
A seven-segment display may have 7, 8, or 9 leads on the chip. Usually leads 8
and 9 are decimal points. The figure below is a typical component and pin layout
for a seven segment display.
7 SEGMENT DISPLAY
The light emitting diodes in a seven-segment display are arranged in the figure
below.
DIODE PLACEMENT IN A SEVEN SEGMENT DISPLAY, NO DECIMAL
There are two types of displays available, common anode and common cathode.
The wiring for a common anode is shown below.
COMMON ANODE INTERNAL WIRING
The wiring for the common cathode is shown below.
COMMON CATHODE INTERNAL WIRING
To convert the binary numbers to signals that can drive the L.E.D.s in the display
you need a display driver. In the lab we use an MC14511 chip. The pinouts are
shown below.
U17
1
2
3
4
5
6
7
8
B
C
LT
BI
LE
D
A
GND
Vcc
16
15
f
14
g
13
a
12
b
11
c
10
d
9
e
MC14511
PINOUTS FOR THE MC14511 SEVEN-SEGMENT DISPLAY DRIVER
A, B, C, and, D are the binary inputs.
a, b, c, d, e, f, and g are the driver signals to the display elements.
LT is the Light Test control, turns all segments on, active low.
LE is the latch enable control.
BL blanks all the segments when activated, active low.
The truth table shown below is used to confirm that the digital signal sent to the
display lights up the correct segment.
TRUTH TABLE FOR THE SEVEN-SEGMENT DISPLAY
The internal circuitry and logic gates for the display is shown below.
INTERNAL CIRCUITRY AND LOGIC GATES FOR 7 SEG DISPLAY
The specific seven-segment display used in lab is an LN513RK. The schematic
below is similar to the one you will use in lab.
SEVEN SEGMENT DISPLAY WITH DISPLAY DRIVER
To have the driver convert the binary input to signals ready for the display, tie pin
3, LT, and pin 4, Bl, to VCC. Connect pin 5, LE, to ground. In this configuration
what ever the binary inputs at A-D are will be converted and the display will show
the decimal equivalent.
COUNTING 0-9
5V
1
0-9 circuit
2
CL
15
9
CLK
CO
LD
10
VCC
7
TE
VCC
PE
1
6
14
13
12
11
7
16
a
P4
Q1
Q2
Q3
Q4
A
Vcc
1
2
14
5
B
C
b
P3
13
4
a
3
P2
6
12
12
P1
D
b
11
c
3
4
5
c
10
10
14161
LT
BI
LE
d
9
d
2
3
4
5
9
10
11
12
5V
e
15
4
1
1A
1B
1C
1D
2A
2B
2C
2D
f
14
e
16
1Y
8
g
2
CAT4
11
GND
f
CAT3
5
CAT2
MC14511-b
13
g
CAT1
3
13
6
9
2Y
LDP
RDP
SEVSEG-b
14012-chip
0-9 COUNTING CIRCUIT
The start of this circuit is the MC14161 binary counter. The function generator is
connected to the clock input to start the counting cycle. The MC14012 NAND
gate monitors the output of the binary counter. When the count equals 9 the
output of the NAND gate sends a signal to the load control, LD, on the counter to
load the values on P1-P4, in this case the number zero. As the counter is
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