One solution, if you don’t have enough IO ports to spare, is to use another Display, like serial cellphone displays, which are cheap and color is a great thing to show off. Or you can expand the number of IO lines by using a shift register or TWI device. This is one such implementation using a 74hc164 shift register. It is based on an implementation by Peter Dannegger. If you prefer to use a 4094 cmos shift register, there are also schematics floating around the net.

The idea behind this implementation is to fill the shift register from the microcontroller using hard- or softspi, then toggle the hd44780′s enable pin. While toggling, the data pin determines the R/S state of the display.

The demo software will print a hello world message onto the display, it is written for AVR microcontrollers, it should work – after modifying the ports and pin numbers – on almost any AVR. Peter Daneggers original software is written for 8051 µCs, I don’t know of any code for PICs.

lcd.tar.bz2

lcdshift.pdf

lcdshift.sch

lcdshift.brd