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Interfacing LCD with PIC problem

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Cantafford

Member
Hello,

I'm trying to interface an LCD with a PIC. I've done this before and had no problems. But now I can't get some text to pop on my LCD.
This is how I interfaced the LCD on PORTB as default:


I'm just trying to get some simple text on the LCD to see it works. I wrote this code:
Code:
#include <stdio.h>
#include <stdlib.h>
#include "header.h"
#include <plib/delays.h>
#include <plib/xlcd.h>

void init_XLCD(void);              // prototypes
void DelayFor18TCY( void );       
void DelayPORXLCD (void);         
void DelayXLCD (void);

void main()
{
    OSCCON = 0x76;
    init_XLCD();
    while(1)
    {
     putrsXLCD("Calculator");
    }
}

void init_XLCD(void) // We initialize the LCD display
{
    OpenXLCD(FOUR_BIT&LINES_5X7); // configure LCD in 4-bit Data interface mode
    while(BusyXLCD()); // Check if the controller's busy before writing any commands
    WriteCmdXLCD(0x06); // move cursor right, don't shift display
    WriteCmdXLCD(0x0C); // turn display on without cursor
}

void DelayFor18TCY(void) // a 18 cycle delay
{
Nop( ); Nop( ); Nop( ); Nop( );
Nop( ); Nop( ); Nop( ); Nop( );
Nop( ); Nop( ); Nop( ); Nop( );
Nop( ); Nop( );
return;
}

void DelayPORXLCD(void) // delay 15ms
{
Delay1KTCYx(30);
}

void DelayXLCD(void) // delay 5ms
{
    Delay1KTCYx(10);
}
This is the header file:
Code:
// PIC18F4550 Configuration Bit Settings

// 'C' source line config statements

#include <xc.h>

// #pragma config statements should precede project file includes.
// Use project enums instead of #define for ON and OFF.

// CONFIG1L
#pragma config PLLDIV = 1       // PLL Prescaler Selection bits (No prescale (4 MHz oscillator input drives PLL directly))
#pragma config CPUDIV = OSC1_PLL2// System Clock Postscaler Selection bits ([Primary Oscillator Src: /1][96 MHz PLL Src: /2])
#pragma config USBDIV = 1       // USB Clock Selection bit (used in Full-Speed USB mode only; UCFG:FSEN = 1) (USB clock source comes directly from the primary oscillator block with no postscale)

// CONFIG1H
#pragma config FOSC = INTOSCIO_EC// Oscillator Selection bits (Internal oscillator, port function on RA6, EC used by USB (INTIO))
#pragma config FCMEN = OFF      // Fail-Safe Clock Monitor Enable bit (Fail-Safe Clock Monitor disabled)
#pragma config IESO = OFF       // Internal/External Oscillator Switchover bit (Oscillator Switchover mode disabled)

// CONFIG2L
#pragma config PWRT = OFF       // Power-up Timer Enable bit (PWRT disabled)
#pragma config BOR = OFF        // Brown-out Reset Enable bits (Brown-out Reset disabled in hardware and software)
#pragma config BORV = 3         // Brown-out Reset Voltage bits (Minimum setting)
#pragma config VREGEN = OFF     // USB Voltage Regulator Enable bit (USB voltage regulator disabled)

// CONFIG2H
#pragma config WDT = OFF        // Watchdog Timer Enable bit (WDT disabled (control is placed on the SWDTEN bit))
#pragma config WDTPS = 32768    // Watchdog Timer Postscale Select bits (1:32768)

// CONFIG3H
#pragma config CCP2MX = ON      // CCP2 MUX bit (CCP2 input/output is multiplexed with RC1)
#pragma config PBADEN = OFF     // PORTB A/D Enable bit (PORTB<4:0> pins are configured as digital I/O on Reset)
#pragma config LPT1OSC = OFF    // Low-Power Timer 1 Oscillator Enable bit (Timer1 configured for higher power operation)
#pragma config MCLRE = OFF      // MCLR Pin Enable bit (RE3 input pin enabled; MCLR pin disabled)

// CONFIG4L
#pragma config STVREN = ON      // Stack Full/Underflow Reset Enable bit (Stack full/underflow will cause Reset)
#pragma config LVP = ON         // Single-Supply ICSP Enable bit (Single-Supply ICSP enabled)
#pragma config ICPRT = OFF      // Dedicated In-Circuit Debug/Programming Port (ICPORT) Enable bit (ICPORT disabled)
#pragma config XINST = OFF      // Extended Instruction Set Enable bit (Instruction set extension and Indexed Addressing mode disabled (Legacy mode))

// CONFIG5L
#pragma config CP0 = OFF        // Code Protection bit (Block 0 (000800-001FFFh) is not code-protected)
#pragma config CP1 = OFF        // Code Protection bit (Block 1 (002000-003FFFh) is not code-protected)
#pragma config CP2 = OFF        // Code Protection bit (Block 2 (004000-005FFFh) is not code-protected)
#pragma config CP3 = OFF        // Code Protection bit (Block 3 (006000-007FFFh) is not code-protected)

// CONFIG5H
#pragma config CPB = OFF        // Boot Block Code Protection bit (Boot block (000000-0007FFh) is not code-protected)
#pragma config CPD = OFF        // Data EEPROM Code Protection bit (Data EEPROM is not code-protected)

// CONFIG6L
#pragma config WRT0 = OFF       // Write Protection bit (Block 0 (000800-001FFFh) is not write-protected)
#pragma config WRT1 = OFF       // Write Protection bit (Block 1 (002000-003FFFh) is not write-protected)
#pragma config WRT2 = OFF       // Write Protection bit (Block 2 (004000-005FFFh) is not write-protected)
#pragma config WRT3 = OFF       // Write Protection bit (Block 3 (006000-007FFFh) is not write-protected)

// CONFIG6H
#pragma config WRTC = OFF       // Configuration Register Write Protection bit (Configuration registers (300000-3000FFh) are not write-protected)
#pragma config WRTB = OFF       // Boot Block Write Protection bit (Boot block (000000-0007FFh) is not write-protected)
#pragma config WRTD = OFF       // Data EEPROM Write Protection bit (Data EEPROM is not write-protected)

// CONFIG7L
#pragma config EBTR0 = OFF      // Table Read Protection bit (Block 0 (000800-001FFFh) is not protected from table reads executed in other blocks)
#pragma config EBTR1 = OFF      // Table Read Protection bit (Block 1 (002000-003FFFh) is not protected from table reads executed in other blocks)
#pragma config EBTR2 = OFF      // Table Read Protection bit (Block 2 (004000-005FFFh) is not protected from table reads executed in other blocks)
#pragma config EBTR3 = OFF      // Table Read Protection bit (Block 3 (006000-007FFFh) is not protected from table reads executed in other blocks)

// CONFIG7H
#pragma config EBTRB = OFF      // Boot Block Table Read Protection bit (Boot block (000000-0007FFh) is not protected from table reads executed in other blocks)

#define __XTAL_FREQ 8000000
When I simulate the code in proteus no text pops on the LCD. Am I missing something?
 

Cantafford

Member
Solved. For some reason(God knows why) when I set frequency oscillator via osccon higher than 4Mhz the text on shopw up on LCD. Any frequency lower than that will do the trick. As I won't be needing a high frequency in my application(I want to do a simple calculator with a 4x4 keyboard) I just lowered it to 4Mhz.

I would like to understand why this happens though if someone has any ideea. Thank you!
 
Last edited:

atferrari

Well-Known Member
I am not conversant in C at all. Maybe your delays are based on the xtal or clock frequency and become too short if the frequency exceeds a certain value. My ex used to say I was always wrong. It could be case here too.
 

Daniel Wood

Member
Glad you fixed it.. Keep in mind that D0-D3 don't like to be left floating in real world applications and should be tied low.

Its hard to tell when using an external library to control the LCD.. My guess is that pin D7 is never being read as a busy flag, so at high speeds, the microcontroller is firing instructions to the LCD faster than the LCD can handle.

When you change OSCCON, do you change the __XTAL_FREQ as well?

Also keep in mind that the DelayFor18TCY() takes 18uS @ 4Mhz.. but delays will be shorter as you up the osc speed.. Same goes for Delay1KTCYx() functions as well
 

spec

Well-Known Member
Most Helpful Member
Solved. For some reason(God knows why) when I set frequency oscillator via osccon higher than 4Mhz the text on shopw up on LCD. Any frequency lower than that will do the trick. As I won't be needing a high frequency in my application(I want to do a simple calculator with a 4x4 keyboard) I just lowered it to 4Mhz.

I would like to understand why this happens though if someone has any idea. Thank you!
I suspect that the problem you experienced may be connected with the hardware.

You do not show the physical layout of your circuit, but long leads, relatively high resistance contacts (as in prototype boards), and the routing of the 0V lines and positive supply lines can cause problems.

Also, the supply lines need to be decoupled physically close to both the PIC18F4550 and the LM016L LCD: 100nF, disk ceramic capacitors (not surface mount) of X7R dielectric, +-10% or better, 10V or higher, would be suitable.

spec
 
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