Page 158 - ARM Based Microcontroller Projects Using MBED

144 8. INTERMEDIATE LEVEL PROJECTS

{
Segments = LEDS[Digits[3]]; // Send to PORT C
Enable3 = Enable; // Enable Digit 3
wait(0.005); // Wait 5ms
Enable3 = Disable; // Disable Digit 3

Segments = LEDS[Digits[2]]; // Send to PORT C
Enable2 = Enable; // Enable Digit 2
wait(0.005); // Wait 5ms
Enable2 = Disable; // Disable Digit 2

Segments = LEDS[Digits[1]]; // Send to PORT C
Enable1 = Enable; // Enable Digit 1
wait(0.005); // Wait 5ms
Enable1 = Disable; // Disable Digit 1

Segments = LEDS[Digits[0]]; // Send to PORT C
Enable0 = Enable; // Enable Digit 0
wait(0.005); // Wait 5ms
Enable0 = Disable; // Disable Digit 0
}
}

FIG. 8.10, CONT’D

There are several algorithms for extracting the digits of an integer number. In this project,
the number to be displayed cannot be greater than four digits long. Assuming that the num-
ber CNT is, for example, 2356, the digits are extracted as follows:

Calculations Digits Extracted
Digits[3]¼CNT/1000; Digits[3]¼2 (MSD)
Y¼CNT 1000*Digits[3]; Y¼356
Digits[2]¼Y/100; Digits[2]¼3
W¼Y 100*Digits[2]; W¼56
Digits[1]¼W/10; Digits[1]¼5
Digits[0]¼W% 10; Digits[0]¼6 (LSD)

8.3.7 Modified Program
The program in Fig. 8.10 displays the leading zeroes. For example, number 10 is displayed
as 0010. We can remove the leading zeroes by disabling their digit. For example, when
displaying “0010,” we can disable the Enable3 and Enable2 digits so that the display shows
“10” and not “0010.” The program given in Fig. 8.11 (program: SevenSegMux5) shows how
the leading zeros can be disabled.

8.3.8 Suggestions for Additional Work
Modify the program as shown in Fig. 8.10 to display the letters “HELO.”