Analog-to-Digital Converter - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 614

buf[4*i 1 2] 5 ATD0DR2;

buf[4*i 1 3] 5 ATD0DR3;

}

asm ( “swi” );

}

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Example 12.8
▼

Write a C program to be run on the Dragon12 demo board to display the voltage (output of
a potentiometer) connected to the AN7 pin. Configure the AD0 properly, perform five conver-
sions per second, and display the voltage on the LCD.
Solution: The conversion result 1023 corresponds to 5 V. Therefore, we need to divide the con-
version result by 204.6 to convert the result back to voltage. Since the HCS12 does not support
floating-point operation directly, we multiply the conversion result by 10 and then divide the
product by 2046 to obtain the voltage value. The C program is as follows:
#include “c:\cwHCS12\include\hcs12.h”
#include “c:\cwHCS12\include\delay.h” // include delay.c in the project

#include “c:\cwHCS12\include\lcd_util.h” // include lcd_util.c in the project

void openAD0(void);
main(void)
{

char buffer[6]; /* used to hold the voltage value */

int temp;

char *msg1 5 “Voltage 5 ”;

openlcd();

buffer[1] 5 '.'; /* decimal point */

buffer[3] 5 0x20; /* space character */

buffer[4] 5 'V'; /* volt character */

buffer[5] 5 0; /* null character */

openAD0();

while(1) {

ATD0CTL5 5 0x87; /* convert AN7, result right-justified */

while(!(ATD0STAT0 & SCF)); /* wait for conversion to complete */

buffer[0] 5 0x30 1 (ATD0DR0 * 10 )/2046;

temp 5 (ATD0DR0 * 10) % 2046; /* find the remainder */

buffer[2] 5 0x30 1 (temp * 10)/2046; /* compute the fractional digit */

cmd2lcd(0x80); /* set LCD cursor to upper left corner*/

puts2lcd(msg1); /* output the message “voltage 5 ” */

puts2lcd(&buffer[0]); /* output voltage string */

delayby100ms(2); /* wait for 200 ms */

}

return 0;

}
void openAD0 (void)
{

int i;

ATD0CTL2 5 0xE0; /* enable AD0, fast ATD flag clear, disable AD0 in wait mode */