The Microcontroller Idea Book - Jan Axelson's Lakeview Research

Chapter 8
Table 8-3. Initialization procedure for LCD modules using HD44780
controller.
Power on
Wait 15 milliseconds after V+ = 4.5V
Function set = 30h
Wait 4.1 milliseconds
Function set = 30h
Wait 100 microseconds
Function set = 30h
Function set to match display module
Display on
Display clear
Entry mode set
set I equal to the instruction and call subroutine 900, which clears RS, writes the instruction
to the display, and toggles E.
Using the example program as a model, you can experiment with your own messages by
adapting the code in lines 400-530.
Listing 8-5 is another test program that displays a prompt on the host’s screen and then
displays the character you type at the keyboard both on the host’s screen and on the LCD
module. To use this program, you must add lines 10 through 380 of Listing 8-4 to initialize
the module and variables.
The 4-bit Interface
The HD44780’s 4-bit data interface can be convenient if you don’t have a lot of port bits to
spare. The minimum interface requires just 6 outputs, to D4-D7, RS, and E. The drawback is
that the 4-bit interface is slower in operation and more complicated to program.
To send an instruction using a 4-bit interface, you send half at a time over D4-D7, along with
the appropriate RS and R/W signals. D0-D3 are unused. For example, with an 8-bit interface,
writing Z (5Ah) to the display requires the following operations:
clear R/W
set RS
write 5Ah to D0-D7
bring E high, then low
148 The Microcontroller Idea Book