Analog-to-Digital Converter - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 626

5 V

HCS12

27 k Ω

10 k Ω

R f

ASCX30AN

+12 V

10 k Ω

1.6 k Ω

V OUT

- +12 V

R 1

-

741

5 V

V M AN7

741

+

+

Offset adjust 3.9 k Ω

R 2

- 12 V

- 12 V

5 V

Figure 12.22 ■ Barometric pressure sensor output scaling and shifting circuit

The barometric pressure ranges from 948 to 1083.8 mbar. The A/D conversion result will
be 0 and 1023 for these two values. Therefore, the A/D conversion result needs to be divided by
7.53 in order to find the corresponding barometric pressure. The following equation shows the
conversion:
Barometric pressure 5 948 1 A/D result/7.53
≈ 948 1 (A/D result 3 100)/753
The C program that performs A/D conversion, translates the result into barometric pres-
sure, converts the barometric pressure into an ASCII string, and then displays the pressure on
the LCD is as follows:
#include “c:\cwHCS12\include\hcs12.h”

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

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

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

void openAD0(void);
char buf[12];
char *msg1 5 “pressure 5 ”;
char *blanks 5 “ ”;
void main (void)

{

unsigned int quo,rem,frem;

long temp;

char *ptr,fdigit;

delayby100ms(2); /* wait for LCD kit to self-initialize */

openlcd(); /* configure LCD kit */

openAD0(); /* configure AD0 module */

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

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

while(1) {

ATD0CTL5 5 0x87; /* start a conversion with result right-justified */

while(!(ATD0STAT0&SCF)); /* wait until conversion is done */

temp 5 (long)ATD0DR0 * 100;

quo 5 temp/753; /* integer part of pressure */