A 16x2 LCD means it can display 16 characters per line and there are 2 such lines. In this LCD each character is displayed in 5x7 pixel matrix. This LCD has two registers.
1. Command/Instruction Register - stores the command instructions given to the LCD. A command is an instruction given to LCD to do a predefined task like initializing, clearing the screen, setting the cursor position, controlling display etc.
2. Data Register - stores the data to be displayed on the LCD. The data is the ASCII value of the character to be displayed on the LCD.
Commonly used LCD Command codes:
Command to LCD Instruction Register
Clear screen display
Display ON, Cursor ON
Force the cursor to the beginning of the 1st line
Force cursor to the beginning of the 2nd line
Use 2 lines and 5x7 matrix
The pin description of this module is given below.
Main power supply
Power supply to control contrast
Contrast adjustment by providing a variable resistor through VCC
RS=0 to select Command Register
RS=1 to select Data Register
R/W=0 to write to the register
R/W=1 to read from the register
A high to low pulse (minimum 450ns wide) is given when data is sent to data pins
To display letters or numbers, their ASCII codes are sent to data pins (with RS=1). Also instruction command codes are sent to these pins.
8-bit data pins
1. Data pin8 (DB7) of the LCD is busy flag and is read when R/W = 1 & RS = 0. When busy flag=1, it means that LCD is not ready to accept data since it is busy with the internal operations. Therefore before passing any data to LCD, its command register should be read and busy flag should be checked.
2. To send data on the LCD, data is first written to the data pins with R/W = 0 (to specify the write operation) and RS = 1 (to select the data register). A high to low pulse is given at EN pin when data is sent. Each write operation is performed on the positive edge of the Enable signal.
3. To send a command on the LCD, a particular command is first specified to the data pins with R/W = 0 (to specify the write operation) and RS = 0 (to select the command register). A high to low pulse is given at EN pin when data is sent.
Displaying single character ‘A’ on LCD
The LCD is interfaced with microcontroller (AT89C51). This microcontroller has 40 pins with four 8-bit ports (P0, P1, P2, and P3). Here P1 is used as output port which is connected to data pins of the LCD. The control pins (pin 4-6) are controlled by pins 2-4 of P0 port. Pin 3 is connected to a preset of 10k? to adjust the contrast on LCD screen. This program uses the above concepts of interfacing the LCD with controller by displaying the character ‘A’ on it.