A character LCD is the most basic form of electronic display device widely in use. It consists of 2 rows of 16 columns in each. Normally an LCD module can display 16 characters. LCD modules which can display up to 20 characters are also available. It is the requirement which determines the choice of the LCD module.
There is no limit for a character LCD to display special & custom characters and this is considered as one of the main advantages. A character LCD can be configured in 8 bit or 4-bit mode in which 8 data pins and 4 data pins are used respectively. This feature allows efficient use of the digital I/0 pins of the microcontroller.
LCD modules are available in different dimensions such as 16×2 (16 characters per line can be displayed with 2 such lines) and 20×4 (20 characters can be displayed per line with four such lines). All character LCDs have 16 lines among which 8 lines are data lines (DB0-DB7).
The rests are control lines and supply lines.
D0-D7: data lines
RS: register select
R/ W: read/write mode select line
E: enable line
VDD: supply line
VSS: ground
VEE: contrast adjust
Open-lab uses 16×2 alphanumeric LCD as default display module. This character LCD has 16 columns which can display 16 characters in a line. The module has two such lines. D0-D7 lines of the LCD are used for data transfer between the module and the microcontroller. The module can be interfaced in both the 8-bit mode, in which all 8 data lines are used and in a 4-bit mode in which only 4 lines are required for data transfer. Command mode or data mode are selected according to the signal on the RS line.
Write mode or read mode is selected according to the signal on the R/W line of the module. VSS and VDD are supply lines for the module. Providing a high to low pulse on the Enable pin of the module latches the data on the connected data lines into the appropriate register selected with the signal on the RS line.
The features of a character LCD module make it more suitable for an electronic display than 7 segment displays and other multi-segment display modules. Most importantly the module can be interfaced much easily unlike other modules with no complexity in both hardware and software.The 4-bit mode interfacing of the LCD module enables an efficient method of saving the number of general-purpose I/O pins which is a major criterion for an embedded system designer. There is no limitation in characters which can be displayed using the module. The contrast of the module can be adjusted using the VEE pin of the module and LED backlight which makes the display more bright can be enabled with LED+ and LED- pin.
The above diagram shows the 16×2 alphanumeric LCD module and its associated ports on the OpenLab platform. The VDD and VSS are terminals to supply voltage and ground respectively. VEE is connected to VCC with a variable resistor so that the contrast for the module can be adjusted. The data lines of the module (D0-D7) are connected in default to the pins of LCD1.
The control lines of the LCD such as register select, R/W and Enable are connected to LCD 2 on the OpenLab.
The port which is used as data port in the firmware should be connected to LCD1 and control port should be connected to LCD2.
For further information please refer: character LCD interfacing in 8-bit mode with ATmega32 microcontroller, character LCD interfacing in 4-bit mode with ATmega32 microcontroller.