Introduction:
Seven segment displays are very common for electronic product to display numerical output. Many common devices like calculators, lift, watches, electronic weighing scales, ovens etc use them. A seven-segment display is so named because it is divided into seven different segments that can be switched on or off. It can display digits from 0 to 9 and quite a few characters like A, b, C, ., H, E, e, F, n, o, t, u, y, etc. Knowledge about how to interface a seven segment display to a micro controller is very essential in designing embedded systems.
The Pin Out and Picture of a 7-segment Display:
Two types of 7-segment display
Seven segment displays are of two types, common cathode and common anode. In common cathode type , the cathode of all LEDs are tied together to a single terminal which is usually labeled as ‘com‘ and the anode of all LEDs are left alone as individual pins labeled as a, b, c, d, e, f, g & h (or dot) . In common anode type, the anode of all LEDs are tied together as a single terminal and cathodes are left alone as individual pins.
Interfacing 7 segment display
Below table shows the binary/hex
values for displaying the digits on CommonCathode seven segment display
Below table shows the binary/hex
values for displaying the digits on CommonAnode seven segment display
In multiplexing all displays are connected in parallel to one port and only one display is
allowed to turn ON at a time, for a short period. This cycle is repeated for at a fast rate and due to the persistence of vision of human eye, all digits seems to glow.
The
main advantages of this method are
–Fewer
number of port pins are required .
–Consumes
less power.
–More
number of display units can be interfaced (maximum 24).
Connection Diagram of Multiple 7-segment Display with PIC16F877A
How it works
Let us see how ‘16’
will be displayed in 2 digit display.•Initially the first
display is only activated by making RC.0 low and then digit drive
pattern for “1″ is loaded to the Port D. This condition is
maintained for around 1ms and then RC.0 is made high. Then the second
display is activated by making RC.1 low and then the digit drive pattern for
“6″ is loaded to the port D. This will make the second display to show “6″.
This condition is maintained for another 1ms. This cycle is
repeated and due to the persistence of vision you will feel it as “16″.
Code:
// two digit number using PIC16F877A // 12MHz
void main() {
unsigned int digit;
unsigned int digit2;
unsigned int cnt=0;
char seg[10]={0x3F,0x06,0x5B,0x4F,0x66,0x7D,0x07,0x7F,0x6F};
TRISD = 0; // CONfigure for portD is output
PORTD = 0; // all are PortD are low or zero
TRISC.F0=0; // PORTC-0 Pin is output
TRISC.F1=0; // PORTC-1 is output
PORTC.F0=0; // PIC IS low or zero
PORTC.F1=0; // Pin is low or zero
while(1){
for (cnt=0; cnt<100; cnt++){
digit=cnt/10;
digit2=cnt%10;
PORTD=seg[digit];
portc.f0=1;
portc.f1=0;
delay_ms(100);
PORTD=0x00;
PORTD=seg[digit2];
portc.f0=0;
portc.f1=1;
delay_ms(100);
PORTD=0x00;
}
}
}
Circuit Diagram
