On Thu, 18 Dec 1997 16:54:29 -0500 Tom Sgouros
<tomfool@CIRCUS.GSO.URI.EDU> writes:
>>On Thu, 18 Dec 1997 16:28:09 -0500, GREG OWEN wrote:
>
>> Hi Piclisters For the LCD experts

>> LCD_LINE0 EQU 0x000
>> LCD_LINE1 EQU 0x040
>> LCD_LINE2 EQU 0x014
>> LCD_LINE3 EQU 0x054
>

> LCD_LINE0 EQU 0x000
> LCD_LINE1 EQU 0x040
>
>Now maybe someone else can explain why this makes sense.
>

The 44780 can control up to 2 lines of 40 characters each.  In the case
of 2 lines, the first character of the first line starts at address 0,
and the first character of the second line starts at address 0x40 (64).
There is no RAM between adresses 0x28 and 0x40, since only 40 characters
per line can be displayed.

Where these characters appear on the glass (if at all) depends on how the
LCD panel, 44780, and 44100 driver chips are connected.

In most cases of a 1-line display, the 44780 operates in 1-line mode, and
the starting address is 0.  However, some 16x1 displays are wired as 8x2.
 This eliminates the need for a 44100 driver chip.  In this case, the
first 8 characters start at address 0, and the second 8 start at address
0x40.

In most cases of a 2-line display, the 2-line mode is simply used.  The
first character of the first line is at address 0, and the first
character of the second line is at address 0x40.

On a 4-line display, the 44780 is working in 2-line mode.  For example,
on a 4x20 display, the first 2 lines are actually one line of 40
characters, split in half.  To simplify layout of the LCD glass, it works
best to put the first 100 (5 dots * 20 chars) column drivers on the top
half of the display, and the second 100 at the bottom.  Lines 3 and 4 are
extensions of lines 1 and 2.    Thus the first character of the first
line is at address 0, the second line at address 0x40, the third at 0x14
(0+20), and the fourth at 0x54 (64+20)

The 4x40 display uses 2 44780 controllers, thus it is actually a dual
2x40 display.