Interfacing a Resistive Touch Screen with 18LF4550 and displaying on an 16x2 LCD

[Akhil Mohan]

Hello all,

I am trying to display the touch positions from a resistive touch screen on a 16x2 LCD using PIC18LF4550. I got a sample code from http://www.pyroelectro.com/tutorials/touchscreen_interface_resistive/software.html

I have made few modifications so that I can operate with 18LF4550. I am using HITECH PICC18-PRO compiler. I am not able to understand the code fully esp the importance of the functions void change_led(int); and the Update routine. On power up, it displays X : and Y: and nothing else. I am finding it difficult to trouble shoot and please help me to understand the code and to make it work
The hardware connections are,



The code follows,

#include <p18f4550.h>
#include <delays.h>
#include <htc.h>
#include <stdlib.h>
#include <ctype.h>

#define rs LATCbits.LATC0
#define rw LATCbits.LATC1
#define en LATCbits.LATC2


#define _XTAL_FREQ 20000000
__CONFIG (1, FOSC_HS);
__CONFIG (2, WDTDIS & PWRTEN & BOREN & LVPDIS);

void prnt(unsigned int);
void commd(unsigned int);
void lcd_init(void);
void change_led(int);
void Delay10KTCYx(unsigned char unit);
void Delay1KTCYx(unsigned char unit);

void main(void)
{

int i=0;
int result_x=0;
int result_y=0;
char x_axis[6];
char y_axis[6];
nRBPU = 1;

//ADCON1 = 0b00000000;

TRISA = 0x00;
TRISB = 0x0F;
TRISC = 0x00;
TRISD = 0x00;

PORTA = 0x03;
PORTB = 0x00;
PORTC = 0x00;
PORTD = 0x00;

Delay10KTCYx(200);

lcd_init();

prnt('X');
prnt(':');
commd(0b11000000); //Move 2nd Next Line

prnt('Y');
prnt(':');
commd(0b10000011);

while(1)
{
//Set PORTA To Inputs/High Impedance
TRISAbits.TRISA0 = 1;
TRISAbits.TRISA1 = 1;

//Set Lower 2 Bits to High Impedance
TRISBbits.TRISB0 = 1;
TRISBbits.TRISB3 = 1;
//Set Higher 2 Bits to Output
TRISBbits.TRISB1 = 0;
TRISBbits.TRISB2 = 0;

PORTBbits.RB0 = 0;
//Provide GND To X-axis Of Touch Screen
PORTBbits.RB1 = 0;
//Provide Power To X-axis Of Touch Screen
PORTBbits.RB2 = 1;
PORTBbits.RB3 = 0;

// configure A/D convertor
ADCON0 = 0x05;
ADCON1 = 0x00;
ADCON2 = 0x82;
Delay10KTCYx( 5 ); // Delay for 50TCY
GO_nDONE = 1; // Code for starting A/D conversion
while (GO_nDONE != 0); // Wait until the A/D conversion is over
result_y = ADRESH; // Read result
//ADON = 0; // ADC is disabled

//Set PORTA To Inputs/High Impedance
TRISAbits.TRISA0 = 1;
TRISAbits.TRISA1 = 1;

//Set Lower 2 Bits As Outputs
TRISBbits.TRISB0 = 0;
TRISBbits.TRISB3 = 0;
//Set Higher 2 Bits to High Impedance
TRISBbits.TRISB1 = 1;
TRISBbits.TRISB2 = 1;

//Provide Power To Y-axis Of Touch Screen
PORTBbits.RB0 = 0;
PORTBbits.RB1 = 0;
PORTBbits.RB2 = 0;
//Provide Ground To Y-axis Of Touch Screen
PORTBbits.RB3 = 1;

ADCON0 = 0x01;
ADCON1 = 0x00;
ADCON2 = 0x82;
Delay10KTCYx( 5 ); // Delay for 50TCY
GO_nDONE = 1; // Code for starting A/D conversion
while (GO_nDONE != 0); // Wait until the A/D conversion is over
result_x = ADRESH; // Read result
//ADON = 0; // ADC is disabled

//Clear Everything In Port C
PORTB = 0x00;
//All High Impedance Outputs
TRISBbits.TRISB0 = 1;
TRISBbits.TRISB1 = 1;
TRISBbits.TRISB2 = 1;
TRISBbits.TRISB3 = 1;

//Don't Display If X or Y Axis Not Active
if( (result_x > 80 && result_x < 900 ) )
{

/******** X-Axis Update ALL *********/
itoa( result_x, x_axis,8);

for(i=0;i<4;i++)
{
//Update Display
if(isalnum(x_axis[i]))
{
prnt(x_axis[i]);
}
else
{
prnt(0x20);
}
}
commd(0b11000011); //Go To 2nd Line 4th Character

/******** Y-Axis Update ALL *********/
itoa( result_y, y_axis,8);

for(i=0;i<4;i++)
{
//Update Display
if(isalnum(y_axis[i]))
{
prnt(y_axis[i]);
}
else
{
prnt(0x20);
}
}
//Short Delay
Delay10KTCYx(10);
//Back To First Line, 4th Character
commd(0b10000011);
}
else
{
Delay10KTCYx(10);
prnt(0x20);
prnt(0x20);
prnt(0x20);
prnt(0x20);
commd(0b11000011);
prnt(0x20);
prnt(0x20);
prnt(0x20);
prnt(0x20);
commd(0b10000011);
}
}
}

void change_led(int result)
{

if(result > 30 && result < 90){

PORTBbits.RB0 = 1;
PORTBbits.RB1 = 0;
}

else if(result > 100 && result < 140){

PORTBbits.RB0 = 1;
PORTBbits.RB1 = 1;
}

if(result > 150 && result < 190){

PORTBbits.RB0 = 0;
PORTBbits.RB1 = 1;
}

if(result > 200 && result < 250)
{
PORTBbits.RB0 = 0;
PORTBbits.RB1 = 0;
}
}

void lcd_init(void)
{
en = 0;
rs = 0;
rw = 0;

Delay10KTCYx( 10 );  // 20ms delay

commd(0x38); // Set interface to 8-bit
Delay10KTCYx( 5 );   // 10ms delay

commd( 0x38 ); // Set interface to 8-bit
Delay10KTCYx( 1 );   // 2ms delay

commd( 0x38 ); // Set interface to 8-bit
Delay10KTCYx( 1 );   // 2ms delay

commd( 0x28 ); // Set interface to 4-bit

commd( 0x2C ); // Function Set

commd(0x0C); // Display On and Cursor Off

commd(0x01); // Clear display screen
Delay10KTCYx( 5 );   // 10ms delay

commd(0x06); // Increment cursor
}

//4-bit print interface
void prnt(unsigned int character)
{
PORTD=character >> 4;

rs = 1;
rw = 0;
en = 1;
en = 0;

PORTD=character & 0x0f;

rs = 1;
rw = 0;
en = 1;
en = 0;

Delay1KTCYx(1);
}

//4-bit instruction interface
void commd(unsigned int commd)
{
PORTD=commd >> 4;
rs = 0;
rw = 0;
en = 1;
en = 0;
PORTD=commd &0x0f;
rs = 0;
rw = 0;
en = 1;
en = 0;
Delay1KTCYx(1);
}

Thanks in Advance
Akhil

 

[Akhil Mohan]

No response, pretty bad situation for me then :sad:

 

[Golden Electronics]

Change_led or update not used in main so u may add it in ur main code or ignore it

 

[Akhil Mohan]

Change_led or update not used in main so u may add it in ur main code or ignore it

Yea, you are right, but that is not going to solve my problem, trying to display the touch co ordinates on LCD

Thanks for you suggestion