►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.
Example:
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 Aug 01 2016, 03:25 PM
Manu Mishra
hi guys if u need c code for SD card interfacing with p89v51rd2 8051 controller system u can see the video of the project and the download the c code form blog http://embeddedinrajasthan.blogspot.in/?view=classic
Mon Aug 01 2016, 03:23 PM
Manu Mishra
hi guys if u need c code for finger print security system u can see the video of the project and the download the c code form blog http://embeddedinrajasthan.blogspot.in/?view=classic
ExperimenterUK
Tue Jul 19 2016, 05:59 PM
@mhammad 64 bits is 8 bytes.
Tue Jul 19 2016, 07:56 AM
mhammad kassem
hello! i want to know how to use UART in mikroc , I want to receive 64 bits from another microcontroller and i dont know how to start my code to receive the 64 bits...any help?
ExperimenterUK
Mon Jul 18 2016, 08:32 PM
@meena.. are you still having trouble ?
Sat Jul 16 2016, 10:19 AM
Meena
problem in loading email address while registering.Please help
Sun Jul 10 2016, 02:50 PM
shockwave
could you please provide a sample code that controling LED using bluetooth HC-05 interfacing pic16f877a thank you!
Sun Jul 10 2016, 02:49 PM
shockwave
Help!
ExperimenterUK
Sat Jul 09 2016, 05:25 PM
@Santhana krishnan post in forum to discuss your problem
Thu Jul 07 2016, 09:26 AM
Santhana krishnan
Hi i program atmega 32 it was functiining corectly but now aref pins voltage 2.56 is droped to .85 volts also a ports input viltage also dropped so anologe inpit not funcitonig please help me to find out the problem

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rajavarmanslr Avatar
Posted By rajavarmanslr
Thu Aug 18 2016, 01:40 PM
I have two 8051 that interfaces with nRF24l01. One...
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Posted By rajavarmanslr
Thu Aug 18 2016, 12:31 PM
I have two 8051 that interfaces with nRF24l01. One...
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Posted By ExperimenterUK
Mon Aug 01 2016, 05:26 AM
is working nowugoo5000Great, thanks for letting u...
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Posted By ugoo5000
Sat Jul 30 2016, 07:31 AM
is working noworg 00hmov p1,#11111111bmov p3,#1111...
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Posted By ugoo5000
Sat Jul 30 2016, 06:40 AM
when i press a button in p3.0,the counter will st...
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Posted By ugoo5000
Sat Jul 30 2016, 06:30 AM
proteus file Attachment ...
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Posted By ExperimenterUK
Fri Jul 29 2016, 11:34 PM
Your code does not count at all, it produces a one...
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Posted By ugoo5000
Fri Jul 29 2016, 07:49 PM
i want the the counter to be counting in secs with...
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Posted By ExperimenterUK
Fri Jul 29 2016, 07:31 PM
HiYour Proteus file did not upload, be sure to zip...
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Posted By ugoo5000
Fri Jul 29 2016, 11:50 AM
below is the proteus file