Page 296 - ARM Based Microcontroller Projects Using MBED

282 10. USING LIQUID CRYSTAL DISPLAYS (LCDs)

10.1.1 HD44780 LCD Module
Although there are several types of LCDs, the HD44780 is currently one of the most pop-
ular LCD modules used in industry and also by hobbyists. This module is an alphanumeric
monochrome display and comes in different sizes. Modules with 16 columns are popular in
most small applications, but other modules with 8, 20, 24, 32, and 40 columns are also avail-
able. Although most LCDs have two lines (or rows) as the standard, it is possible to purchase
models with one or four lines. The LCD displays are available with standard 14-pin connec-
tors, although 16-pin modules are also available, providing terminals for backlighting.
Table 10.1 illustrates the pin configuration and pin functions of a 14-pin LCD module. A brief
summary of the pin functions is given below:
V SS (pin 1) and V DD (pin 2) are the ground and power supply pins. Although the manufac-
turersspecify5VDCsupply,themoduleswillusuallyworkwithaslowas3.6Vorashighas6V.
V EE is pin 3 and this is the contrast control pin used to adjust the contrast of the display. The
arm of a 10K potentiometer is normally connected to this pin and the other two terminals of
the potentiometer are connected to the ground and power supply pins. The contrast of the
display is adjusted by rotating the potentiometer arm.
Pin 4 is the Register Select (RS) and when this pin is LOW, data transferred to the display is
treatedascommands.WhenRSisHIGH,characterdatacanbetransferredtoandfromthedisplay.
Pin 5 is the Read/Write (R/W) line. This pin is pulled LOW in order to write commands or
character data to the LCD module. When this pin is HIGH, character data or status informa-
tion can be read from the module. This pin is normally connected permanently LOW so that
commands or character data can be sent to the LCD module.

TABLE 10.1 Pin Configuration of HD44780 LCD Module
Pin No Name Function
1 V SS Ground
2 V DD +ve supply
3 V EE Contrast
4 RS Register select
5 R/W Read/write
6 E Enable
7 D0 Data bit 0
8 D1 Data bit 1
9 D2 Data bit 2
10 D3 Data bit 3
11 D4 Data bit 4
12 D5 Data bit 5
13 D6 Data bit 6
14 D7 Data bit 7