Brief Overview about Hitachi HD44780

Standard Controller for Dot Matrix LCDs

Table of Contents [Toc]

Terminology
Correspondence between Character Codes and Character Patterns
Relationship between CGRAM Addresses, Character Codes (DDRAM) and Character Patterns (CGRAM Data)
Initializing the LCD by Instruction
   8 bit Interface
   4 bit Interface
 

This is only a short reference for the most important commands not mentionned
in "The Extended Concise LCD Data Sheet".

Terminology   [Toc] [Top]

Correspondence between Character Codes and Character Patterns
(ROM Code: A00)   [Toc] [Top]

Note: The user can specify any pattern for character-generator RAM (8 different characters).

Relationship between CGRAM Addresses, Character Codes (DDRAM)
and Character Patterns (CGRAM Data)   [Toc] [Top]

Notes:

1. Character code bits 0 to 2 correspond to CGRAM address bits 3 to 5 (3 bits: 8 types).
2. CGRAM address bits 0 to 2 designate the character pattern line position. The 8th line is the
    cursor position and its display is formed by a logical OR with the cursor.
3. Character pattern row positions correspond to CGRAM data bits 0 to 4 (bit 4 being at the left).
4. As shown Table 5, CGRAM character patterns are selected when character code bits 4 to 7
    are all 0. However, since character code bit 3 has no effect, the R display example above
    can be selected by either character code 00H or 08H.

Notes:

1. Character code bits 1 and 2 correspond to CGRAM address bits 4 and 5 (2 bits: 4 types).
2. CGRAM address bits 0 to 3 designate the character pattern line position. The 11th line
    is the cursor position and its display is formed by a logical OR with the cursor.
    Since lines 12 to 16 are not used for display, they can be used for general data RAM.
3. Character pattern row positions are the same as 5 X 8 dot character pattern positions.
4. CGRAM character patterns are selected when character code bits 4 to 7 are all 0.
    However, since character code bits 0 and 3 have no effect, the P display
    example above can be selected by character codes 00H, 01H, 08H, and 09H.

Initializing the LCD by Instruction (Software Reset)   [Toc] [Top]

If the power supply conditions for correctly operating the internal reset circuit are not met,
initialization by instructions becomes necessary.
This procedure must take place in a software reset on a 4 bit Interface
to assure proper re-entry to the LCD communication.

Refer to the initialization procedure of my LCD assembler module files, e.g. m_lcd.asm.
 

8 bit Interface   [Toc] [Top]

4 bit Interface   [Toc] [Top]

Last updated: 31.12.2004