HD44780 Character LCD Displays Tutorial

Posted on Feb 5, 2014

Interfacing with a HD44780 compatible display using some DIP switches and a few other components. The module that we are using is a 16 character x 2 line display that we stock over here. It uses an ST7065C controller, which is HD44780 compatible. The figure below shows the LCD module and pinout. The circuit diagram below shows the LCD module with the basic

HD44780 Character LCD Displays Tutorial
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plumbing  wired up. You will notice that pin 5 (RW) is tied to ground. This pin is use to control whether you are reading or writing to the display. Since reading from the display is very rare, most people just tie this pin to ground. Data and commands are sent to the module using the 8 data lines (pins 7-14) and the RS line (pin 4). The RS lines tells the module whether the 8 data bits relate to data or a command. The data/command is read on the falling edge of the enable line (pin 6). This means that when enable transitions from high to low, the values of D0 to D7 and RS are read. There are minimum wait times between these operations, but I won`t go into them here. You can look these up in the LCD Module Datasheet. (look at the timing diagrams on page 4) HD44780 based display modules also have a 4 bit interface mode. Under this mode the data or command is transferred to the module using 2, 4 bit nibbles. This will be discussed in more detail below. Normally you would drive an LCD display from a microcontroller, computer or similar device. For this exercise we will use just a series of switches. This cuts the interface to the absolute bare essentials. The photo below shows the circuit, on a breadboard without the LCD module. I`ve also added a small L7805 based power supply on the right hand side of the board. You can get the parts for the power supply here. The Register Select and data lines are pulled down using a 10K...

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