The LCDs have a parallel interface, meaning that the microcontroller has to manipulate several interface pins at once to control the display. The interface consists of the following pins:
– A register select (RS) pin that controls where in the LCD’s memory you’re writing data to. You can select either the data register, which holds what goes on the screen, or an instruction register, which is where the LCD’s controller looks for instructions on what to do next.
– A Read/Write (R/W) pin that selects reading mode or writing mode
– An Enable pin that enables writing to the registers
– 8 data pins (D0 -D7). The states of these pins (high or low) are the bits that you’re writing to a register when you write, or the values you’re reading when you read.
– There’s also a display contrast pin (Vo), power supply pins (+5V and Gnd) and LED Backlight (Bklt+ and BKlt-) pins that you can use to power the LCD, control the display contrast, and turn on and off the LED backlight, respectively.