**user**

http://www.eetasia.com/ARTICLES/2004...URCES=DOWNLOAD

Before you start reading the touchscreen coordinates, you need to know if the screen has been touched. By having 5V at Y+ and 0V at X- you monitor if the screen was touched. The setup is as follows

And the code is

START: '################ START READING AVERAGE PRESSURE VALUE ################ TRISA = 001001 ' Set Y+ (portA.2, AN2) and X- (portA.1, AN1) as outputs ' and Y- (portA.3, AN3) and X+ (portA.0, AN0) as inputs low PORTA.1 ' Set X- = 0V high PORTA.2 ' Set Y+ = 5V ADCON0 = 000001 ' Bits(5-2): 0000=AN0. Start sampling at X+ pauseus 10 ADCON0.1 = 1 ' Stops or continues sampling depending on ADCON2 bits(5-3), ' then begins conversion GOSUB CONVERSION_ROUTINE ' Obtain value for A/D conversion resolution PRESSURE_XP = RESOLUTION ' Obtain PRESSURE_XP from X+ sampling, X- = 0V, and Y+ = 5V ADCON0 = 001101 ' Bits(5-2): 0011=AN3. Start sampling at Y- pauseus 10 ADCON0.1 = 1 ' Stops or continues sampling depending on ADCON2 bits(5-3), ' then begins conversion GOSUB CONVERSION_ROUTINE ' Obtain value for A/D conversion resolution PRESSURE_YM = RESOLUTION ' Obtain PRESSURE_YM from Y- sampling, X- = 0V, and Y+ = 5V IF (PRESSURE_XP > 24) AND (PRESSURE_YM < 1000) THEN ' THE TOUCHSCREEN HAVE BEEN TOUCHED GOSUB READ_COORDINATES gosub CONVERT_TO_PIXELS ENDIF LCDOUT $FE, 1 ' Clear LCD LCDOUT $FE,2,"X=",DEC5 X_VALUE,", Y=",DEC5 Y_VALUE ' DISPLAYS A/D CONVERSION VALUES LCDOUT $FE,$C0,"P1=",DEC4 PRESSURE_XP,", P2=",DEC4 PRESSURE_YM GOTO START

**PRESSURE_XP**is going to be very close to zero and the reading for

**PRESSURE_YM**is going to be very close to 1024, remember it is a 10-bit ADC. The screen has been touched when the following condition has been met

IF (PRESSURE_XP > 24) AND (PRESSURE_YM < 1000) THEN ' THE TOUCHSCREEN HAVE BEEN TOUCHED

And the code is

'**************************************************************** '* READ X AND Y VALUES SUBROUTINE * '**************************************************************** READ_COORDINATES: ' PORTA.0 (AN0) -> X+ ' PORTA.1 (AN1) -> X- ' PORTA.2 (AN2) -> Y+ ' PORTA.3 (AN3) -> Y- '################ READ AVERAGE X-VALUE ################ TRISA = 000011 ' Set X+ (portA.0, AN0) and X- (portA.1, AN1) as inputs ' and Y+ (portA.2, AN2) and Y- (portA.3, AN3) as outputs low PORTA.3 ' Set Y- = 0V high PORTA.2 ' Set Y+ = 5V ADCON0 = 000001 ' Bits(5-2): 0000=AN0. Start sampling at X+ pauseus 10 ADCON0.1 = 1 ' Stops or continues sampling depending on ADCON2 bits(5-3), ' then begins conversion GOSUB CONVERSION_ROUTINE ' Obtain value for A/D conversion resolution X_VALUE = RESOLUTION ' Obtain X_VALUE from X+ sampling, Y- = 0V, and Y+ = 5V ADCON0 = 000101 ' Bits(5-2): 0001=AN1. Start sampling at X- pauseus 10 ADCON0.1 = 1 ' Stops or continues sampling depending on ADCON2 bits(5-3), ' then begins conversion GOSUB CONVERSION_ROUTINE ' Obtain value for A/D conversion resolution X_VALUE = (X_VALUE + RESOLUTION) ' Obtain X_VALUE from X- sampling, Y- = 0V, and Y+ = 5V '################ READ AVERAGE Y-VALUE ################ TRISA = 001100 ' Set X+ (portA.0, AN0) and X- (portA.1, AN1) as outputs ' and Y+ (portA.2, AN2) and Y- (portA.3, AN3) as inputs low PORTA.1 ' Set X- = 0V high PORTA.0 ' Set X+ = 5V ADCON0 = 001001 ' Bits(5-2): 0010=AN2. Start sampling at Y+ pauseus 10 ADCON0.1 = 1 ' Stops or continues sampling depending on ADCON2 bits(5-3), ' then begins conversion GOSUB CONVERSION_ROUTINE ' Obtain value for A/D conversion resolution Y_VALUE = RESOLUTION ' Obtain Y_VALUE from Y+ sampling, X- = 0V, and X+ = 5V ADCON0 = 001101 ' Bits(5-2): 0011=AN3. Start sampling at Y- pauseus 10 ADCON0.1 = 1 ' Stops or continues sampling depending on ADCON2 bits(5-3), ' then begins conversion GOSUB CONVERSION_ROUTINE ' Obtain value for A/D conversion resolution Y_VALUE = (Y_VALUE + RESOLUTION) ' Obtain Y_VALUE from Y- sampling, X- = 0V, and X+ = 5V RETURN '**************************************************************** '* CONVERSION SUBROUTINE * '**************************************************************** CONVERSION_ROUTINE: REPEAT ' Wait until conversion is finished. When finished ADCON0.1 will be =0 PAUSEUS 10 CONV_STATUS = ADCON0.1 UNTIL CONV_STATUS = 0 RESOLUTION.BYTE0 = ADRESL : RESOLUTION.BYTE1 = ADRESH ' READ A/D CONVERSION VALUE RETURN

'**************************************************************** '* CONVERT_TO_PIXELS ROUTINE * '**************************************************************** CONVERT_TO_PIXELS: 'Ax, Bx, Ay, and By should be found experimentally X_VALUE =Ax* X_VALUE +BxY_VALUE =Ay* Y_VALUE +ByRETURN

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