►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.




◄ Previous Page  |  Next Page ►

Back To Index

Conversation

hiast
Thu Jun 16 2016, 03:03 PM
help please how do i initiate port 3 as an input port in assembly? acutely there is push switch connecting to p3.2 push switch connecting to p3. 3 push switch connecting to p3.4 push switch connecting to p3.5 and i need to call function when the user pressed the push switch for the previous pins (not used as counter and not as timer… just call a function ( do special thing) when any push switch is pressed ???????
Mon Jun 06 2016, 12:02 PM
nida hussain
hi.. i need some help with keypad interfacing code.like i want to write a code in c language that takes an input of 2 digit numbers from a keypad interfaced with 8051 mc and stores the entered values in some array
Sat May 28 2016, 04:34 PM
kibrom berhe
c code for locker security system based on rfid and gsm
ExperimenterUK
Wed May 25 2016, 05:05 AM
@ Ramanjaneyulu, post in forum,explain your problem
Mon May 23 2016, 11:34 PM
Ramanjaneyulu
Hi, I Am using at89c4051 for my application, I want 5u sec dely.. Up to 1milli sec iam able to producing delay. Beyond the 1milli second, I am unable to produce the acceurate dely. Plz any one help me
Sat May 21 2016, 09:51 PM
A K
i want to mak an auto dialer using gsm and atmega 16. please helpe me how to write a code to auto dial a number saved in sim
Sat May 21 2016, 10:42 AM
Alec
Hi im trying to program my 89s51 with a usbasp so any ideas on the circuit?
Wed May 18 2016, 10:08 AM
Tashu joshi
anyone know how to develop
Wed May 18 2016, 10:07 AM
Tashu joshi
i'm working for resporatry system using 8051,
Wed May 18 2016, 10:06 AM
Tashu joshi
i'm developing a respiratory system using Arduino

Downloads

Comments

dyoussef
Wed Jun 29 2016, 07:29 PM
sung7333
Tue Jun 28 2016, 06:23 AM
Bonolai
Fri Jun 24 2016, 06:02 AM
hiast
Sat Jun 11 2016, 02:30 PM
alex1311
Thu Jun 09 2016, 06:57 AM
zaft93
Sun May 15 2016, 01:52 AM
CELEBI
Thu May 12 2016, 08:28 AM
Suro1996
Wed May 11 2016, 06:07 PM

Online

Guests: 38, Members: 0 ...

most ever online: 182184
(Members: , Guests: 182184) on 06 Aug 2010: 05:37 AM

Members: 37770
Newest member: dyoussef
Forum Activity
dyoussef Avatar
Posted By dyoussef
Wed Jun 29 2016, 07:34 PM
Hello, I am referencing this project: http://www.8051projects.net/wiki/I2C_Implementation_on_PICI am using PIC16F1847 and XC8 so I've had to make a few changes to the code. While making changes, my compiler gave me an error for the I2CWait function for the while statement. It says "unexpected token amp". Here is the line in question:while ((SSPCON2 & 0x1F ) || ( SSPSTAT & 0x04 ) );I changed the register names to be consistent with my PIC but it didn't solve the problem.What changes do I need to make to this function so that this error does not occur?
ExperimenterUK Avatar
Posted By ExperimenterUK
Wed Jun 22 2016, 07:54 PM
I can't see why it should work sometimes and not o...
ExperimenterUK Avatar
Posted By ExperimenterUK
Wed Jun 22 2016, 12:58 AM
You could use T0 and T1 to trigger interrupts but ...
Karan123 Avatar
Posted By Karan123
Tue Jun 21 2016, 04:40 AM
I am not Getting you . the project is to interfac...
Karan123 Avatar
Posted By Karan123
Tue Jun 21 2016, 04:34 AM
Hello,Thanks , It Works . Master-Slave address Ma...
alex1311 Avatar
Posted By alex1311
Mon Jun 20 2016, 11:38 AM
Football is my passion and I have dreamt of becomi...
ExperimenterUK Avatar
Posted By ExperimenterUK
Fri Jun 17 2016, 11:00 PM
>But Can't modify code at Receiver End for Differe...
hiast Avatar
Posted By hiast
Fri Jun 17 2016, 03:25 PM
thanks for help,i wanted to write this code as you...
Karan123 Avatar
Posted By Karan123
Fri Jun 17 2016, 12:19 PM
I don't your applications . But below should help ...
Karan123 Avatar
Posted By Karan123
Fri Jun 17 2016, 12:07 PM
I know i have to use below code at Transmitter End...