HD44780 based character LCDs require at least 6 I/O lines from microcontroller to display data. Therefore, they are not suitable for low-pin microcontrollers like PIC12F series microchips. In this project, I am going to show how to drive an HD44780 based LCD display with only 3 pins of a microcontroller. I am going to demonstrate it with PIC12F683 microchip. The character data and command from the microcontroller is transferred serially to a shift register (74HC595), and the parallel output from the shift register is fed to LCD pins.
3-Wire Serial LCD using a Shift Register - [Link]