Interfacing 7-Segment Display using lookup table

by Ranjith | April 28th, 2009.

Calculation of lookup table as follows:

The lookup table contains the input pattern for the LED legs, to display the corresponding digits.

The table shows the seven segment requirement pattern to display the Hex number, with the Seven segment conversion.

For example, Let us consider the display of the number 0, where we need to switch ON all the LEDs which are there at the boundary. i.e. for a CC LED, we should supply 5 volts to these LEDs. The 6 LEDs (‘a’ through ‘f’) should get binary 1, the dot and the (middle) hyphen segment should get 0Volts or the binary Zero. Effectively the Seven segment pattern code will be (0011 1111) 3Fh. That is what we OUT through the port pins.

For a Common Anode LED, the display pattern will be the complement of that of Common Cathode pattern.

For Common Cathode :

Common Cathode Lookup Table

For common Anode:

Common Anode Lookup Table

ASM program:

This program displays characters 0 through 9 on seven-segment display connected directly to the port 2 of the microcontroller Intel8951.

Here, the look up table is stored from the memory location 19H of the microcontroller. The first set is the pattern code for common anode followed by the common cathode.

        //Look up table for common Anode
 
        org 0000
        mov r0,#19h
        mov @r0,#0c0fh             // Code for the digit 0
        inc r0
        mov @r0,#0f9h             // Code for the digit 1
        inc r0
        mov @r0,#0a4h             // Code for the digit 2
        inc r0
        mov @r0,#0b0h             // Code for the digit 3
        inc r0
        mov @r0,#099h             // Code for the digit 4
        inc r0
        mov @r0,#092h             // Code for the digit 5
        inc r0
        mov @r0,#082h             // Code for the digit 6
        inc r0
        mov @r0,#0f8h             // Code for the digit 7
        inc r0
        mov @r0,#0f0h             // Code for the digit 8
        inc r0
        mov @r0,#98h             // Code for the digit 9         
 
        //Look up table for common Cathode
 
        org 0000
        mov r0,#19h
        mov @r0,#0bfh
        inc r0
        mov @r0,#86h
        inc r0
        mov @r0,#0dbh
        inc r0
        mov @r0,#0cfh
        inc r0
        mov @r0,#0e6h
        inc r0
        mov @r0,#0edh
        inc r0
        mov @r0,#fdh
        inc r0
        mov @r0,#87h
        inc r0
        mov @r0,#0ffh
        inc r0
        mov @r0,#0e7h
 
    again: mov a,#00h                         ; Start form zero
       up:  mov r2,a
            mov r0,#19h                       ; Load starting address of luck up table
            add a,r0
            mov r0,a
            mov a,@r0                         ; Get the LED equivalent
            mov p2,a                          ; Move to Port 2
 
           mov r3,#255                        ; Delay
    D1:    mov r1,#255
    D:     djnz r1,D
           djnz r3,D1
           mov a,r2
           inc a
           cjne a,#0ah,up
           sjmp again

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5 Responses to “Interfacing 7-Segment Display using lookup table”

1
nithinissac Says:
May 20th, 2009 at 1:40 pm
need a AT89C51 microcontroller compiler
2
Interfacing 7-segment display using 7447 decoder | electrofriends Says:
August 17th, 2009 at 7:03 pm
[...] Using lookup table. This uses 7 output pins of microcontroller [...]
3
progs Says:
September 10th, 2009 at 7:10 am
do you have pcb diagram of 7 segment
4
RAJESH Says:
April 25th, 2010 at 2:56 pm
its nice.please send me the details about this project.thankuuuu.
my email id:rajeshkannapwf@gmail.com
5
Arvind(B.E I.C) Says:
May 31st, 2010 at 10:19 am
really a nice detail provided…itz working for me…