Seven Segment Board, Getting Started
Seven segment displays are electronic display devices used to display decimal digits as a simpler low cost alternatives to more complex dot matrix displays. The Seven Segment Board, from Zilogic, is an 8 digit seven segment display. In this first article, in a series of articles on the Seven Segment Board, we will introduce the reader to seven segment display fundamentals, and usage of the Seven Segment Board.
Selecting a Digit
A digit of the Seven Segment Board can be selected by using three
control lines DSEL0, DSEL1 and DSEL2. The following table shows
the DSELx pin states, the corresponding digit selected.
| DSEL0 | DSEL1 | DSEL2 | DIGIT Selected |
|---|---|---|---|
| 0 | 0 | 0 |
DIGI1
|
| 0 | 0 | 1 |
DIGI2
|
| 0 | 1 | 0 |
DIGI3
|
| 0 | 1 | 1 |
DIGI4
|
| 1 | 0 | 0 |
DIGI5
|
| 1 | 0 | 1 |
DIGI6
|
| 1 | 1 | 0 |
DIGI7
|
| 1 | 1 | 1 |
DIGI8
|
Displaying a Single Digit
The algorithm for displaying a 7-segment digit is given below.
-
Drive the
DISPON#high to turn off the display. -
Turn on/off segments by driving the segment signals
SEG[A:H]. The segment signals to be driven for each decimal digit is given in the following table. -
Select the 7-segment display by driving
DSEL[0:2] -
Drive the
DISPON#high to turn on the display.
| Character |
SEG[A:H] in Binary
|
SEG[A:H] in Hex
|
|---|---|---|
| 0 |
0b1111_1100
|
0xFC
|
| 1 |
0b0110_0000
|
0x60
|
| 2 |
0b1101_1010
|
0xDA
|
| 3 |
0b1111_0010
|
0xF2
|
| 4 |
0b1010_1010
|
0xAA
|
| 5 |
0b1011_1010
|
0xBA
|
| 6 |
0b1011_1110
|
0xBE
|
| 7 |
0b1110_0000
|
0xE0
|
| 8 |
0b1111_1110
|
0xFE
|
| 9 |
0b1110_0110
|
0xE6
|
The MSB of segment signals (7th bit) is used to switch on the dot separator.
Multiplexed 7-Segment Display
Since the signals that drive the segments are shared by the 8 displays, the segments of only one display can be driven at a time. Each display is turned on successively for a small period of time (1.5ms, to avoid flicker), and by persistence of vision all of them appear to be on simultaneously.
Persistence of vision is the phenomenon of the eye by which even nanoseconds of exposure to an image result in milliseconds of sight. — Wikipedia.org
The algorithm for displaying multiple 7-segment digits simultaneously is given below.
-
Turn off the display.
-
Select the next 7-segment digit.
-
Drive the segment data pins corresponding to the value to be displayed.
-
Turn on the display.
-
Generate a 1.5ms delay using a timer.
-
Goto step a.
Credits
The Seven Segment Digit image is based on this Seven Segment image from Wikimedia Commons.
