BCD to 7 segment decoder | Computer Organization And Architecture Tutorials

In BCD (Binary Coded Decimal), a binary pattern is used to represent a decimal number. A 7 segment display is used to display hexadecimal numeral by seven LEDs arranged in a definite pattern as shown in figure (a).

A BCD to 7 segment decoder accepts the BCD code on its input and provide output to drive a 7 segment display.

For example, if the BCD code in the input is 0011 then we have to display decimal 3 on the 7 segment display. From the figure(b) it is clear that to display a 3 on a seven-segment display we have to enable LEDs a,b,c,d and g. So the output lines should be a=,b=1,g=1,c=1 and d=1.

The truth table for a seven segment decoder is given below,

Decimal Digit	Input				Decoding function	Output
Decimal Digit	A0	A1	A2	A3	Decoding function	a	b	c	d	e	f	g
0	0	0	0	0	${abcdef \overline g}$	1	1	1	1	1	1	0
1	0	0	0	1	${\overline a bc \overline d \overline e \overline f \overline g}$	0	1	1	0	0	0	0
2	0	0	1	0	${ab \overline c de \overline f g}$	1	1	0	1	1	0	1
3	0	0	1	1	${abcd \overline e \overline f g}$	1	1	1	1	0	0	1
4	0	1	0	0	${\overline a bc \overline d \overline e f g}$	0	1	1	0	0	1	1
5	0	1	0	1	${a \overline bcde \overline f g}$	1	0	1	1	0	1	1
6	0	1	1	0	${a \overline b cdefg}$	1	0	1	1	1	1	1
7	0	1	1	1	${abc \overline d \overline e \overline f \overline g}$	1	1	1	0	0	0	0
8	1	0	0	0	${abcdefg}$	1	1	1	1	1	1	1
9	1	0	0	1	${abcd \overline e fg}$	1	1	1	1	0	1	1

Further Reading