Interfacing Seven Segment Display to 8051

8/13/2019 Interfacing Seven Segment Display to 8051

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Interfacing Seven segment display to 8051

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June - 20 - 201222 Comments

A Note about 7 segment LE display!

This article is about how to interface a seven segment LED displa to an !0"1

microcontroller# $ segment LED displa is ver popular and it can displa digits from 0

to % and &uite a few characters li'e () b) C) #) *) E) e) +) n) o)t)u)) etc# ,nowledge abouthow to interface a seven segment displa to a micro controller is ver essential in

designing embedded sstems# ( seven segment displa consists of seven LEDs arranged

in the form of a s&uarish "8#slightl inclined to the right and a single LED as the dotcharacter# Different characters can be displaed b selectivel glowing the re&uired LED

segments# even segment displas are of two tpes) common cathode and common

anode..n common cathode tpe ) the cathode of all LEDs are tied together to a singleterminal which is usuall labeled as /com/ and the anode of all LEDs are left alone asindividual pins labeled as a) b) c) d) e) f) g h or dot # .n common anode tpe) the

anode of all LEDs are tied together as a single terminal and cathodes are left alone as

individual pins# The pin out scheme and picture of a tpical $ segment LED displa isshown in the image below#

$ segment LED displa

igit drive pattern!

Digit drive pattern of a seven segment LED displa is simpl the different logic

combinations of its terminals $a" to $%/ in order to displa different digits and

characters# The common digit drive patterns 0 to % of a seven segment displa areshown in the table below#
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igit a b c d e f g

0 1 1 1 1 1 1 0

1 0 1 1 0 0 0 0

2 1 1 0 1 1 0 1

3 1 1 1 1 0 0 14 0 1 1 0 0 1 1

" 1 0 1 1 0 1 1

5 1 0 1 1 1 1 1

$ 1 1 1 0 0 0 0

! 1 1 1 1 1 1 1

% 1 1 1 1 0 1 1

Interfacing seven segment display to 8051!

.nterfacing $ segment displa to !0"1

The circuit diagram shown above is of an (T!%"1 microcontroller based 0 to % counter

which has a $ segment LED displa interfaced to it in order to displa the count# Thissimple circuit illustrates two things# *ow to setup simple 0 to % up counter using !0"1and more importantl how to interface a seven segment LED displa to !0"1 in order to

displa a particular result# The common cathode seven segment displa D1 is connected

to the 6ort 1 of the microcontroller (T!%"1 as shown in the circuit diagram# 73 to710 are current limiting resistors# 3 is the reset switch and 72)C3 forms a debouncing

circuitr# C1) C2 and 81 are related to the cloc' circuit# The software part of the pro9ect

has to do the following tas's#
http://www.circuitstoday.com/wp-content/uploads/2012/06/interfacing-7-segement-display-to-8051.png


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+orm a 0 to % counter with a predetermined dela around 1:2 second here#

Convert the current count into digit drive pattern#

6ut the current digit drive pattern into a port for displaing#

(ll the above said tas's are accomplished b the program given below#

&rogram!

ORG 000H //initial starting address

START: MOV A,#00001001B // initial value of au!ulator

MOV B,A

MOV R0,#0AH //Register R0 initiali"ed as ounter $i$ ounts fro! 10

to 0

%AB&%: MOV A,B

'() A

MOV B,A

MOV) A,*A+) // adds t$e -.te in A to t$e rogra! ounters address

MOV 1,A

A)A%% &%A // alls t$e dela. of t$e ti!er&) R0//)ounter R0 dere!ented -. 1

MOV A,R0 // R0 !oved to au!ulator to $e2 if it is "ero in ne3t

instrution4

56 START //)$e2s au!ulator for "ero and 7u!s to START4 one to

$e2 if ounting $as -een finis$ed4

S5M %AB&%

B 89H // digit drive attern for 0

B 0H // digit drive attern for 1

B ;BH // digit drive attern for H // digit drive attern for

B 0>H // digit drive attern for >

B >9H // digit drive attern for ?

B 9H // digit drive attern for @

&%A: MOV R=,#0;H // su-routine for dela.

A'T1: MOV R8,#00H

A'T


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.n the program) initial value in ( is 00001001A# E@ecution of ;(?6C will

add oooo1001A to the content in 6C address of ne@t instruction# The result will be the

address of command DA 3+* line1" and the data present in this address ie 3+* digitdrive pattern for 0 gets moved into the accumulator# ;oving this pattern in the

accumulator to 6ort 1 will displa 0 which is the first count#

(t the ne@t count) value in ( will advance to 00001010 and after the e@ecution of

;?6C )the value in ( will be 05* which is the digit drive pattern for 1 andthis will displa 1 which is the ne@t count and this ccle gets repeated for subse&uent

counts#

The reason wh accumulator is loaded with 00001001A % in decimal initiall is that theinstructions from line % to line 1" consumes % btes in total#

The lines 1" to 24 in the program which starts with command DA can be called as a Loo'

(p )able *L()+# Command DA is 'nown as Define Ate B which defines a bte# This

table defines the digit drive patterns for $ segment displa as btes in he@ format#;


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applications# (lso the ma@imum number of displas that can be connected to the !0"1 is

limited to 4 because !0"1 has onl 4 ports# ;ore over three 3 displas will be


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condition is maintained for another 1ms and then port 3#1 is made low# This ccle is

repeated and due to the persistence of vision ou will feel it as 15M#

Transistor N1 drives the first displa D1 and transistor N2 drives the second displaD2# 711 and 712 are the base current limiting resistors of N1 and N2# The purpose of

other components are e@plained in the first circuit#

&rogram!

ORG 000H // initial starting address

MOV 1,#00000000B // lears ort 1

MOV R,#1H // stores 1

MOV R>,#H // stores

MOV 8,#00000000B // lears ort 8

MOV TR,#%AB&%1 // loads t$e adress of line //


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Interfacing Seven Segment Display to 8051