MPXM2102AS datasheet(478/670 Pages) MOTOROLA

478 / 670 page

AN1536

3–332

Motorola Sensor Device Data

www.motorola.com/semiconductors

{

unsigned int cntr;

/* free running timer system counter */

unsigned int r0;

/* difference between cntr and input capture 1 register */

unsigned int r1;

/* difference between cntr and input capture 2 register */

unsigned int r2;

/* difference between cntr and input capture 3 register */

unsigned long difference; /* the difference between the upper and lower

instrument amplifier outputs */

unsigned long int pfs; /* result defined as percent of full scale relative to

the reference voltage */

if (polarity == 1)

/* set the hc4053 configuration */

PORTB &= 0xfe;

/* polarity = 1 means + output of sensor */

else

PORTB |= 0x1;

/* is connected to the upper opamp */

delay();

/* this will allow the hc4053 to stabilize and the cap

to discharge from the previous conversion */

TFLG1=0X07;

/* clear the input capture flags */

cntr=TCNT;

/* get the current count */

PORTA &= 0X7F;

/* turn the fet off */

while ((TFLG1 & 0X7) < 7); /* loop until all three input capture

flags are set */

r0 = TIC1 – cntr;

/* reference voltage */

r1 = TIC2 – cntr;

/* top side of the inst. amp */

r2 = TIC3 – cntr;

/* lower side of the inst. amp */

PORTA |= 0X80;

/* turn the fet on */

if (polarity == 1)

difference = ( r1 + 1000 ) – r2;

else

difference = ( r2 + 1000 ) – r1;

pfs = (difference * 10000) / r0;

if (difference > 32767) /* this will cover up the case

where the a to d computes a

negative value */

pfs=0;

return ( pfs );

}

atod()

/* computes the a/d value in terms of % full scale */

{

unsigned long int x,y,z;

x = convert(1);

/* normal */

y = convert(0);

/* reversed */

z = (x + y)>>1 ;

/* 2x difference / 2

return(z);

/* z is percent of full scale */

}

integrate() /* returns the a/d value in terms of % full scale and computes

offset from calibration values */

{

unsigned long int j;

int i;

j=0;

for (i=0; i<20; ++i)

j +=atod();

j = (j/20) – ADZERO;

/* null out the xdcr zero input offset */

return(j);

}

cala2d()

/* returns the average of 50 raw a/d conversions this is only

used by the calibration functions */

{

unsigned long int j;

int i;

j=0;

for (i=0; i<50; ++i)

{ j +=atod(); }

j=j/50;

return(j);

}

/* ################################################################### */

cvt_bin_dec ( unsigned int arg )

{

char i;

for ( i=0; i < 6; ++i )

Freescale Semiconductor, Inc.

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