There are 2 types of 7 segment displays , Common Anode & Common Cathode.In this post we shall see how to interface a Common Cathode display with 89S52 Microcontroller.

As the name indicates the cathode points of all segments are made common to GND .To make a segment Glow , the corresponding segment pin is made HIGH.

 

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The PORT pins P2.0 to P2.6  are  connected to segments a through  g. The dot pin can be left out.

A NPN transistor is used at the common cathode point . When the base of transistor is made HIGH , it conducts & applies Ground to the Common Cathode point.The transistor is controlled by port pin P1.0

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Following table explains how to arrive at the HEX value for displaying each Digit.

For e.g , to display digit 1 , the segments b & c should be High & all others Low.This corresponds to 0x06 in Hex format.

Similarly to display digit 0 , all segments , except g should be made High, which is hex 0x3F.

For this demo , we do not use the Dot .Hence it is 0 for calculating all other digits.

 

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To start with create a folder say , F:\7segment  to store project files.

Open KEIL click on Project –> New uVision Project & browse to the location of the folder created.Provide a filename & Save.

Select the Target Device as ATMEL AT89S52.

Target1 is created in Project file window of KEIL.

Right click Target 1 & click on “Options for Target Target1”

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On the Options Window select the tab “ OUTPUT”

Check mark the box “Create HEX file” . This step is important & if you forget check marking this box , no HEX file will be generated.

 

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Now to add the C file to project , Right click Source Group 1 & click on “Add new item to Group “l

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Select the first option C File & provide a Name .Click on ADD

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You can see the .C file added to the project .

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Type in the following  code :

—————————————————————

// Port pin P1.0 is used to Enable the 7 segment CC display
//Port pins of P2 are connected to each segment of CC display

#include<reg52.h>
sbit ledenable=P1^0;
void delay(void);

void main()
{
    P2 = 0x00;
    ledenable=0;
while(1)                  //indefinite loop
  {
     ledenable=1;           // Enable pin for Common cathode display
   P2=0x3f;                          //Display digit 0
   delay();
   P2=0x06;                          //Display digit 1
   delay();
   P2=0x5b;                          //Display digit 2
   delay();
   P2=0x4f;                          //Display digit 3
   delay();
   P2=0x66;                          //Display digit 4
   delay();
   P2=0x6d;                          //Display digit 5
   delay();
   P2=0x7c;                          //Display digit 6
   delay();
   P2=0x07;                          //Display digit 7
   delay();
   P2=0x7f;                          //Display digit 8
   delay();
   P2=0x6f;                          //Display digit 9
   delay();
  }
}
void delay(void)
{
    int j;
    int i;
    for(i=0;i<10;i++)
    {
        for(j=0;j<10000;j++)
        {
        }
    }
}

—————————————–

Instead of a long code you can also use Array as below

First initialize all the segment hex values of the digits in an array.

 

unsigned char digit[10]={0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,0x7f,0x67};

Now take for loop and assign array values to the PORT2 with some time delay.

Here is the code using Array :

——————————————————-

#include<reg52.h>

sbit ledenable=P1^0;
void delay();
unsigned char digit[]={0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,0x7f,0x67};
unsigned int k;
void main()
{
    P2 = 0x00;
    ledenable=0;
   
  while(1)                  //indefinite loop
   {
    ledenable=1;         // Enable pin for Common cathode display
    
       for(k=0;k<10;k++)
        {
           P2=digit[k];
           delay();
        }
   }
}

void delay()
{
    int j;
    int i;
    for(i=0;i<10;i++)
    {
        for(j=0;j<10000;j++)
        {
        }
    }
}

———————————————————–

 

After Feeding in the code click on SAVE button & then F7 to build the project.

 

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If all syntax are correct , compiling will be successful.

 

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Inside the Project folder you can see the HEX file created.This is the file we’re going to fuse on the Target chip.

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Connect the ISP board to the Development board & finally connect the USB cable to pc.

Open the PROGISP software .The PRG ISP & USB ASP buttons should be activated.If any one is greyed out then check for the drivers to be installed for the ISP board.

Click on FILE –> LOAD FLASH & browse to the location of the project folder where the HEX file was generated.

Select the HEX file  .Click on AUTO button to perform the programming.

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Once the HEX file is fused , you can see the result on the 7 segment display counting from 0 to 9.

 

7SEG21

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