(From left to right)
Vss- Ground
VDD- Power 5V
VEE- LCD Contrast Adjustment
Control Signals
RS- Register Select
There are 2 very important registers in LCD
- Command Code register
- Data Register
If
RS=0 à Instruction command Code register is selected, allowing user to send command
RS=1 à Data register is selected allowing to send data that has to be displayed.
R\W- Read\Write
R\W input allows the user to write information to LCD or read information from it. How do we read data from LCD????? The data that is being currently displayed will be stored in a buffer memory DDRAM. This data could be read if necessary.
If
R\W=0 à Reading
R\W=1 à Writing
E- Enable
The enable Pin is used by the LCD to latch information at its data pins. When data is supplied to data pins, a high to low pulse must be applied to this pin in order for the LCD to latch the data present in the data pins.
Eà Toggle
Data Bus- D0-D7
Power for Backlighting LEDs
VDD-Power 5V
Vss- GND
General Explanation
We have to prepare an LCD properly before the character we need, has to be displayed. For this a number of commands have to be provided to the LCD before inputting the required data. The commands will be discussed in the later part of this tutorial.
LCD doesn’t know about the content (data or commands) supplied to its data bus. It is the user who has to specify whether the content at its data pins are data or commands. For this, if a command is inputted then a particular combination of 0s and 1s has to be applied to the Control lines so as to specify it is a Command on the other hand if a data is inputted at the data lines then an another combination of 0s and 1s has to be applied to the control lines to specify it is Data. (Hope you are not confused!!!!). The combinations are as follows-
If
Command à RS=0, R\W=0, E=1\0
Dataà RS=1, R\W=0, E=1\0
Various Commands used in LCDs
Interfacing with PIC
Here 2 ports PORT B and PORT C of PIC 16F877A is taken. PORT B is used for providing control signals and PORT C is used for providing Data signals.
Of which pins of PORT B are specified as below.
RB0à RS
RB1à R\W
RB2 à E
Programming Steps
1) Before sending Data to be Displayed to the LCD, it should be prepared to hold that particular value.
2) For this certain initializations are to be done as per the Instructions.
b. Move Value 0X06, 1 time.
c. Move Value 0X0F, 1 time.
3) After each initializations command function and delay should be called.
4) After Initialization Move Data to the LCD
5) Call the Data Function and delay.
( 2 functions , one for command and the other for data is being written for the simplicity of the program)
Program
#include"delay.h"
void main()
{
void command(); //function for command manipolation
void data(); //function for data manipulation
int i;
char a[ ]={"haripanangad"};
TRISC=0X00; //Made Port C Out put port (to use with in main function)
TRISB=0X00; //Made Port B output port (to use with outer function)
DelayMs(1);
PORTC=0X38; //to select the mode of the LED 0X38 - 8 bit 2 lines
command(); // Call command function
DelayMs(1);
PORTC=0X38; //to select the mode of the LED 0X38 - 8 bit 2 lines
command(); // Call command function
DelayMs(1);
PORTC=0X06; // to activate entry mode
command();
DelayMs(1);
PORTC=0X0F; //to get a blinking curser display
command();
DelayMs(1);
for(i=0;i<12;i++)
{
PORTC= a[i];
data(); //To show that the given values are data
DelayMs(1);
}
while(1);
}
void command() //command function definition
{
RB0=0;
RB1=0;
RB2=1;
DelayUs(1);
RB2=0;
}
void data() //data function definition
{
RB0=1;
RB1=0;
RB2=1;
DelayUs(1);
RB2=0;
}
