AN1250 datasheet(7/22 Pages) MICROCHIP

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DS01250A-page 7

AN1250

Example 3 provides the equivalent code for reading the

capacitive touch sensors using the CTMU on a PIC24F

device. Example 4 has the same algorithm for a

PIC18F device. Note that the channel number being

read is referenced by the Index variable. The

ADSELECT

array is setup to have the correct bits set for

the corresponding Index variable so that the correct

channel is set to an analog A/D. The A/D value is

temporarily stored in the variable, immediateValue.

The LoopCount determines how long the CTMU

current source charges the capacitive touch circuit.

EXAMPLE 3:

READING THE CAPACITIVE TOUCH SENSOR CIRCUIT SOFTWARE ALGORITHM

(PIC24F)

//Read CTMU (Get the raw sensor reading)

AD1PCFGL= 0xFFFF;

//set all A/D channels to digital I/O pins

TRISB = 0x0000;

LATB

= 0x0000;

PORTB = 0x0000;

//set all channels to logical 0 outputs

Nop(); Nop(); Nop(); Nop();

//Wait for charge to drain

TRISB = ADSELECT[Index];

//set selected channel to input

AD1PCFGL = ~ADSELECT[Index];

//set selected channel to analog A/D input

Nop(); Nop(); Nop(); Nop();

//wait for A/D to connect to channel

AD1CHS = Index;

//select A/D channel

CTMUCONbits.IDISSEN

= 1;

//Drain any charge on the A/D circuit

Nop(); Nop(); Nop(); Nop(); Nop();

//Wait for charge to drain

CTMUCONbits.IDISSEN = 0;

//Stop discharge of A/D circuit

IFS0bits.AD1IF

= 0;

//Make sure A/D interrupt flag = 0

AD1CON1bits.SAMP

= 1;

//Manually start sampling

CTMUCONbits.EDG2STAT

= 0;

// Make sure edge2 is 0

CTMUCONbits.EDG1STAT

= 1;

// Set edge1 - Start Charge

for (count = 0; count < loopCount; count++);

// Delay for CTMU charge time

CTMUCONbits.EDG1STAT

= 0;

//Clear edge1 - Stop Charge

IFS0bits.AD1IF

= 0;

AD1CON1bits.SAMP

= 0;

//Clear SAMP bit to begin manual A/D conversion

while(!IFS0bits.AD1IF);

//Wait for the A/D conversion to finish

immediateValue = ADC1BUF0;

//Read the value from the A/D conversion

AD1CON1bits.SAMP

= 0;

IFS0bits.AD1IF

= 0;

AD1CON1bits.DONE

= 0;

//Make sure A/D bits are cleared

//End of CTMU read

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