The Microcontroller Idea Book - Jan Axelson's Lakeview Research

Table 8-1. LCD modules containing the HD44780 controller often use this
14-line interface.
Displays
Pin Symbol Input/
Output
Function
1 VSS Input Signal Ground
2 VDD Input Supply Voltage (+5V)
3 V0 Input Contrast adjust
4 RS Input Register select (1=data; 0=instruction
register, busy flag/address counter)
5 R/W Input Read (1)/write (0) select
6 E Input Enable
7 D0 I/O Data bit 0
8 D1 I/O Data bit 1
9 D2 I/O Data bit 2
10 D3 I/O Data bit 3
11 D4 I/O Data bit 4
12 D5 I/O Data bit 5
13 D6 I/O Data bit 6
14 D7 I/O Data bit 7
Memory Areas
The HD44780’s on-chip memory includes a CG (character-generator) ROM, CG RAM, DD
(display data) RAM, an instruction register, and a data register.
The CG ROM stores the segment patterns for generating 192 different characters, including
the Roman (English) alphabet in upper and lower case, numbers, some math and other
special symbols, and Japanese kana characters. These are fixed in ROM and can’t be altered.
The CG RAM stores segment patterns for up to 16 user-designed characters such as logos,
special symbols, or other simple graphics characters that you design on the 5 X 8 matrix.
To create a custom character, you write a series of 5-bit words to the CG RAM. Each word
represents the segment pattern for one row in the desired character. The patterns stored in
CG RAM disappear on powering down, so you must reload them on each time you power
up.
The Microcontroller Idea Book 141