Theory for interfacing LCD

LCD interfacing theory

In this tutorial I will show you the operation modes of LCD then describe how to program and interface an LCD with 8051 using C language.

Operation of LCD

Now a day’s LCD is finding widespread use replacing LEDs (7 segment LEDs or other multi 7 segment LEDs). For the following reasons………

1.      The declining or lower price of LCDs.

2.      Wide range of use (ability to display numbers, characters, and graphics). This is in contrast to LEDs, which are limited to numbers and a few characters.

3.      Incorporation of refreshing controller into the LCD, thereby relieving the CPU of the task of refreshing the LCD. In contrast, the LED must be refreshed by the CPU (or in some other way) to keep displaying the data.

4.      Ease of programming for characters and graphics.

LCD pin description

Pin	Symbol	I/O	Description
1	Vss	-	GND
2	Vcc	-	+5V power supply
3	Vee	-	Power supply to control contrast
4	RS	I	RS=0 to select command register RS=1 to select data register
5	R/W	I	R/W=0 for write, R/W=1 for read
6	E	I/O	Enable
7	DB0	I/O	The 8-bit data bus
8	DB1	I/O	The 8-bit data bus
9	DB2	I/O	The 8-bit data bus
10	DB3	I/O	The 8-bit data bus
11	DB4	I/O	The 8-bit data bus
12	DB5	I/O	The 8-bit data bus
13	DB6	I/O	The 8-bit data bus
14	DB7	I/O	The 8-bit data bus

RS register select

There are two important registers inside the LCD. The RS pin is used for their selection as follows. If RS=0, the instruction command code register is selected, allowing the user to send a command such as clear display, cursor at home, etc. If RS=1 the data register is selected, allowing the user to send data to be displayed on the LCD.

RW, read write

R/W input allows the user to write information to the LCD or read information from it. R/W = 1 when reading; R/W = 0 when writing.

E enable

The enable pin is used by the LCD latch information presented to 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 in the data present at the data pins. This pulse must be a minimum of 450 ns wide.

LCD Command Codes

HEX Code
1	Clear display screen
2	Return Home
4	Shift cursor to left
5	Shift display right
6	Shift cursor to right
7	Shift display left
8	Display off, cursor off
A	Display off, cursor on
C	Display on, cursor off
E	Display on, cursor blinking
F	Display off, cursor off
10	Shift cursor position to left
14	Shift cursor position to right
18	Shift the entire display to the left
1C	Shift the entire display to the right
80	Cursor to beginning of 1st line
C0	Cursor to beginning of 2nd line
38	2 lines and 5x7 matrix