Experiment No. 3: LCD Interface in 4-bit Mode

The objective of this experiment is to interface a 16x2 LCD to PIC16F628A in 4-bit mode. This means the data transfer will use only four pins of the microcontroller. There is no additional hardware setup needed for this experiment, as we have a ready-made LCD interface female header. We only need to define the data transfer and control pins in the software. Remember, the LCD interface in our development board uses the following pins of PIC16F628A:

Data Transfer : D4 -> RB4, D5 -> RB5, D6 -> RB6, D7 -> RB7

RS -> RA0, and EN -> RA1

Circuit Diagram:

For those who want to do this on a protoborad, here is the circuit:

Software:

 Note: Never forget to disable the comparator functions on PORTA.0, 1, 2, 3 pins if you are going to use those pins as digital I/O.

/*
 * Project name:
     Test LCD in 4-bit mode
 * Copyright:
     (c) Rajendra Bhatt, 2009.
 * Description:
     This code demonstrates how to display test message on a LCD which
     is connected to PIC16F628A through PORTB. D4-D7 pins of LCD are
     connected to RB4-RB7, whereas RS and EN pins connected to RA0 and RA1
     respectively.
     MCU:             PIC16F628A
     Oscillator:      XT, 4.0 MHz
*/
// LCD module connections
sbit LCD_RS at RA0_bit;
sbit LCD_EN at RA1_bit;
sbit LCD_D4 at RB4_bit;
sbit LCD_D5 at RB5_bit;
sbit LCD_D6 at RB6_bit;
sbit LCD_D7 at RB7_bit;
sbit LCD_RS_Direction at TRISA0_bit;
sbit LCD_EN_Direction at TRISA1_bit;
sbit LCD_D4_Direction at TRISB4_bit;
sbit LCD_D5_Direction at TRISB5_bit;
sbit LCD_D6_Direction at TRISB6_bit;
sbit LCD_D7_Direction at TRISB7_bit;
// End LCD module connections
// Define Messages
 char message1[] = "Testing LCD";
 char message2[] = "using PIC16F628A";
 char message3[] = "Test Successful!";
 char message4[] = "2009/09/18";
void main() {
  CMCON  |= 7;                       // Disable Comparators
  Lcd_Init();                        // Initialize LCD
  do {
  Lcd_Cmd(_LCD_CLEAR);               // Clear display
  Lcd_Cmd(_LCD_CURSOR_OFF);          // Cursor off
  Lcd_Out(1,1,message1);             // Write message1 in 1st row
  Lcd_Out(2,1,message2);             // Write message1 in 2nd row
  Delay_ms(2000);
  Lcd_Cmd(_LCD_CLEAR);               // Clear display
  Lcd_Out(1,1,message3);             // Write message3 in 1st row
  Lcd_Out(2,1,message4);
  Delay_ms(2000);
  } while(1);
}

Experiment Output Video:



If you don't see any message on the display, try adjusting the contrast level using Contrast Adjustment Potentiometer.