Digital Electronics
Electronics Technology
Landon Johnson
Encoding, Decoding, and
Seven-Segment Displays
Encoder/Decoder Competencies
52. Given four different input combinations to a 10 line to 4 line
encoder, the student will state the output combinations with
100% accuracy.
53. Given four different input combinations for a 4 line to 10
line decoder, the student will state the output combinations
with 100% accuracy.
Encoder/Decoder Vocabulary
ENCODER- a digital circuit that produces a
binary output code depending on which of its
inputs are activated.
DECODER- a digital circuit that converts an
input binary code into a single numeric
output.
ENCODERS AND DECODERS
A0
O0
A0
O0
A1
A2
A3
O1
O2
A1
A2
O1
O2
O3
ENCODER
DECODER
A4
O4
A5
A6
O5
O6
A7
O7
ONLY ONE INPUT
ACTIVATED AT A TIME
BINARY CODE OUTPUT
BINARY CODE INPUT
ONLY ONE OUTPUT
ACTIVATED AT A TIME
THE 8421 BCD CODE
• BCD stands for Binary-Coded Decimal.
• A BCD number is a four-bit binary group that
represents one of the ten decimal digits 0 through 9.
Example:
Decimal number 4926
4
9
2
6
8421 BCD coded number 0100 1001 0010 0110
ELECTRONIC ENCODER DECIMAL TO BCD
BCD output
Decimal input
7
5
3
00
11
01
0
Decimal
to
BCD
Encoder
0
• Encoders are available in IC form.
• This encoder translates from decimal
input to BCD output.
10 line to 4 line Encoder
10 line to 4 line Encoder
BINARY (BCD)
DECIMAL
8
ENCODER
9 5V
8 5V
7 5V
6 5V
5 5V
4 5V
3 5V
2 5V
1 5V
74147
I9
I8
I7
I6
I5
I4
I3
I2
I1
A3
A2
A1
A0
4
2
1
4 line to 10 line Decoder
DECIMAL
9
8
BINARY (BCD)
8 0V
4 0V
2 0V
1 0V
DECODER
7
74LS42
9
8
7
6
5
4
A3
3
A2
2
A1
1
A0
0
6
5
4
3
2
1
0
DECODERS: BCD TO
7-SEGMENT DECODER/DRIVER
Decimal output
LED
BCD input
0 10 01 01
BCD-to7-Segment
Decoder/
Driver
• Electronic decoders are available in IC form.
• This decoder translates from BCD to decimal.
• Decimals are shown on an 7-segment LED display.
• This IC also drives the 7-segment LED display.
TEST
Q #5#1- What is the decimal output from the decoder that
#2#3#4appears on the 7-segment display?
Answer: 6
3
0
9
7
BCD input
Decimal output
010 100 010 0110
BCD-to7-Segment
Decoder/
Driver
?
BCD-TO-SEVEN SEGMENT DECODER DRIVER
V+
abcdef g .
5V
74LS47
A3
g
A2
f
A1
e
A0
d
c
b
a
test
RBI RBO
TEST
A0
O0
A1
O1
A2
O2
A3
A4
A5
A6
A7
A8
A9
ENCODER
O3
INPUT
A1=1
A4=1
A6=1
A8=1
O3
O2
O1
O0
TEST
A0
O0
A1
O1
A2
O2
A3
DECODER
O3
O4
O5
O6
O7
O8
O9
A3
0
0
0
1
A2
0
1
1
0
A1
0
0
1
0
A0
0
1
1
1
OUTPUT
TEST
ANSWER THE FOLLOWING QUESTIONS WITH ONE OR MORE
OF THESE WORDS: MUX, DEMUX, ENCODER, DECODER.
A. Has more inputs than outputs. ENCODER, MUX
B. Uses select inputs. MUX, DEMUX
C. Can be used in parallel-to-serial conversion. MUX
D. Produces a binary code at its output. ENCODER
E. Only one of its outputs is activated at one time. DEMUX, DECODER
F. Used to route input signals to one of several outputs. MUX
G. Used to generate arbitrary logic functions. MUX, DEMUX
H. 3 line-to-8 line or binary to octal. DECODER
I. Data Selectors are also MUX.