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Microcontroller 7 Segment Interfacing

http://www.shree-electronics.com/images/DSC00209.JPG

Seven segment display is a basic type of display which can display numbers from 0 to 9. The circuit for interfacing single 7 segment display is shown below.

http://www.shree-electronics.com/images/7_segment_small.gif

Driving a 7 segment display is as simple as flashing LEDs, but here we are flashing 7+1 LEDs. The 7 segment display module has 8 LEDs (7 segments to display number and one segment for decimal point or dot) arranged in a particular manner as shown in image below.

http://www.shree-electronics.com/images/7_segment_display.svg.png

http://www.shree-electronics.com/images/commom_cathode1.gif http://www.shree-electronics.com/images/commom_anode1.gif

By driving (in the sense controlling ON and OFF conditions) these LEDs in various combinations, we can display the numbers 0 to 9. There are basically two types of 7 segment displays, they are common cathode and common anode. In common cathode, the cathodes of all the LED segments are connected together, we should apply a logic 1 or high input to a segment pin to light up that particular segment, and in common cathode the case is opposite. Table below shows the combinations of inputs to be applied to 7 segment display for digits 0 to 9.

For common cathode displays
Digit binary input value hexadecimal input value
0 11111100 FC
1 01100000 60
2 11011010 DA
3 11110010 F2
4 01100110 66
5 10110110 B6
6 10111110 BE
7 11100000 E0
8 11111110 FE
9 11110110 F6

For common anode displays
Digit binary input value hexadecimal input value
0 00000011 03
1 10011111 9F
2 00100101 25
3 00001101 0D
4 10011001 99
5 01001001 49
6 01000001 41
7 00011111 1F
8 00000001 01
9 00001001 09

The images shown below are the photographs of 7 segment add-on board for my microcontroller board, I have included one 7 segment in the current version of my development board, so if you are using that circuit then you don’t need an external 7 segment display board. Click on the image to enlarge.

http://www.shree-electronics.com/images/DSC00045_small.JPG http://www.shree-electronics.com/images/DSC00261_small.JPG

The assembly language source code for interfacing 7 segment display is given below.

;*************************************************
;
;Program: Driving seven segment display
;Author: Srikanth
;Website: http://shree-electronics.com/
;Description: Displays numbers 0 to 9 on
;the LED seven segment display continuously
;
;*************************************************

;Declarations
port equ P0

;*************************************************

;Main program
org 0000h
ljmp main
org 30h

main:mov r0,#08h
mov a,#00000001b ;test all segments of disp
up: rr a
mov port,a
acall delay
djnz r0,up

again:mov port,#11111100b ;’0′
acall delay
mov port,#01100000b ;’1′
acall delay
mov port,#11011010b ;’2′
acall delay
mov port,#11110010b ;’3′
acall delay
mov port,#01100110b ;’4′
acall delay
mov port,#10110110b ;’5′
acall delay
mov port,#10111110b ;’6′
acall delay
mov port,#11100000b ;’7′
acall delay
mov port,#11111110b ;’8′
acall delay
mov port,#11110110b ;’9′
acall delay
sjmp again

;*************************************************

delay:mov r2,#0ffh ;delay subroutine
up3: mov r4,#03fh
up2: mov r3,#0fh
up1: djnz r3,up1
djnz r4,up2
djnz r2,up3
ret

;*************************************************

end


April 11, 2010 - Posted by | Microcontroller Interfacing |

2 Comments »

  1. THIS SITE HAS BEEN SO USEFUL TO ME IN MY PROJECT WORK,IN DESIGN AND CONTRUCTION OF 7 SEGMENT DIPLAY OF DIGITAL ANENOMETER.

    Comment by CHIDOLUE | March 17, 2011

  2. neeh and what for 2 digits counter?

    Comment by Me | January 30, 2013


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