►Seven-Segment Display Example

The segments in a 7-segment display are arranged to form a single digit from 0 to F. We can display a multi-digit number by connecting additional displays. Even though LCD displays are more comfortable to work with, 7-segment displays are still standard in the industry. This is due to their temperature robustness, visibility and wide viewing angle. Segments are marked with non-capital letters: a, b, c, d, e, f, g and dp, where dp is the decimal point. The 8 LEDs inside each display can be arranged with a common cathode or common anode. With a common cathode display, the common cathode must be connected to the 0V rail and the LEDs are turned on with a logic one. Common anode displays must have the common anode connected to the +5V rail. The segments are turned on with a logic zero. The size of a display is measured in millimeters, the height of the digit itself (not the housing, but the digit!). Displays are available with a digit height of 7,10, 13.5, 20, or 25 millimeters. They come in different colors, including: red, orange, and green.

The simplest way to drive a display is via a display driver. These are available for up to 4 displays. Alternatively displays can be driven by a microcontroller and if more than one display is required, the method of driving them is called "multiplexing."

The main difference between the two methods is the number of "drive lines." A special driver may need only a single "clock" line and the driver chip will access all the segments and increment the display. If a single display is to be driven from a microcontroller, 7 lines will be needed plus one for the decimal point. For each additional display, only one extra line is needed. To produce a 4, 5 or 6 digit display, all the 7-segment displays are connected in parallel. The common line (the common-cathode line) is taken out separately and this line is taken low for a short period of time to turn on the display. Each display is turned on at a rate above 100 times per second, and it will appear that all the displays are turned on at the same time. As each display is turned on, the appropriate information must be delivered to it so that it will give the correct reading. Up to 6 displays can be accessed like this without the brightness of each display being affected. Each display is turned on very hard for one-sixth the time and the POV (persistence of vision) of our eye thinks the display is turned on the whole time. Therefore, the program has to ensure the proper timing, else the unpleasant blinking of display will occur.

Connecting a microcontroller to 7- segment displays in multiplex mode

Program "7seg.asm" displays decimal value of a number stored in variable D.
movlw .21 	 
movlw D 	; number 21 will be printed on 7seg display

Displaying digits is carried out in multiplex mode which means that the microcontroller alternately prints ones digit and tens digit. TMR0 interrupt serves for generating a time period, so that the program enters the interrupt routine every 5ms and performs multiplexing. In the interrupt routine, first step is deciding which segment should be turned on. In case that the tens digit was previously on, it should be turned off, set the mask for printing the ones digit on 7seg display which lasts 5ms, i.e. until the next interrupt.

For extracting the ones digit and the tens digit, macro digbyte is used. It stores the hundreds digit, the tens digit, and the ones digit into variables Dig1, Dig2, and Dig3. In our case, upon macro execution, Dig1 will equal 0, Dig2 will equal 2, and Dig3 will equal 1.

The following example shows the use of the macro in a program. Program prints a specified 2-digit number on a 7seg display in multiplex mode.

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Mon Mar 27 2017, 04:09 AM
priyanja awate
my project is greenhouse monitering and controlling using 8051 .can u give me the program of this project
Sat Mar 25 2017, 09:56 PM
@Noreen I suggest you log in and post a full description of what you need in our PIC forum
Sat Mar 25 2017, 03:10 PM
Hello I worked on a project related to Wireless Electricity theft detection using GSM during my bachelors. I used Nokia 6230 for sending sms using AT commands. I chose to work with SMS text mode. The microcontroller I used was PIC16F877A and its software coding done through PIC Basic Pro. Unfortunately, I lost my account password and do not have coding for generation sms using AT commands. I need that coding. Can some one help me to provide complete Pic Basic Pro code. In which step by step guidance is given so that I can understand easily. Regards,
Wed Mar 22 2017, 09:13 PM
ajay kumar
help me nokia lcd light
Wed Feb 22 2017, 06:14 AM
Indeed, on the LCD tutorial, many missing Tables and figures !!
Wed Feb 22 2017, 06:06 AM
I don't see any Table 3. I'm using Chrome.
Fri Feb 03 2017, 05:56 AM
irfan shaikh
hi, i want interface WS2811 pixel led using NUVOTON N79E352, but i dont know how to code it. can anyone help me or provide me sample coding for interfacing WS2811 PIXEL LED. THNX
Thu Jan 19 2017, 08:42 PM
Hi...i have made a circuit for interfacing PT100 with LM358 whose temperature is shown on the LCD...But the temperature is not getting incresed slowly ..a small change directly increses the temp...can any one help me
Thu Jan 19 2017, 04:27 PM
send me alarm clock simulation using proteus software
Mon Jan 16 2017, 03:15 PM
How can we read notepad file using random acess file



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I have attached code showing one method you could ...
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I am using Keil and 8051 microcontroller
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The best way is to use an interrupt to run the cou...
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You have largely answered your own question.Use on...
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