Книга: Advanced PIC Microcontroller Projects in C

HD44780 LCD Module

HD44780 LCD Module

The HD44780 is one of the most popular alphanumeric LCD modules and is used both in industry and by hobbyists. This module is monochrome and comes in different sizes.

Table 6.10: Pin configuration of HD44780 LCD module

Modules with 8, 16, 20, 24, 32, and 40 columns are available. Depending on the model chosen, the number of rows may be 1, 2, or 4. The display provides a 14-pin (or 16-pin) connector to a microcontroller. Table 6.10 gives the pin configuration and pin functions of a 14-pin LCD module. The following is a summary of the pin functions:

VSS is the 0V supply or ground. The V_DD pin should be connected to the positive supply. Although the manufacturers specify a 5V DC supply, the modules will usually work with as low as 3V or as high as 6V.

Pin 3, named V_EE, is the contrast control pin. This pin is used to adjust the contrast of the display and should be connected to a variable voltage supply. A potentiometer is normally connected between the power supply lines with its wiper arm connected to this pin so that the contrast can be adjusted.

Pin 4 is the register select (RS), and when this pin is LOW, data transferred to the display is treated as commands. When RS is HIGH, character data can be transferred to and from the module.

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 information can be read from the module.

Pin 6 is the enable (E) pin, which is used to initiate the transfer of commands or data between the module and the microcontroller. When writing to the display, data is transferred only on the HIGH-to-LOW transition of this line. When reading from the display, data becomes available after the LOW-to-HIGH transition of the enable pin, and this data remains valid as long as the enable pin is at logic HIGH.

Pins 7 to 14 are the eight data bus lines (D0 to D7). Data can be transferred between the microcontroller and the LCD module using either a single 8-bit byte or as two 4-bit nibbles. In the latter case, only the upper four data lines (D4 to D7) are used. The 4-bit mode means that four fewer I/O lines are used to communicate with the LCD. In this book we are using only an alphanumeric-based LCD and only the 4-bit interface.

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