Re: Byte structure of Lo res

[heuser.marcus@freenet.de]

> Unfortunately I don't know how the text is, wish I had a //e technical
> reference.  So a nibble is the color part?  0-15?  It starts at $0400 right?
> Are there two screens?  With the other at $0800?  Is it scrambled like
> hi-res?

The text mode is "colorless": A byte is a single character - thats all
(8 bits).

In lores-mode this byte is split into two big pixels (4 bits each = 16
colors). 4 bits are simply called a "nibble" (like 8 bits are called a
"byte").

The addressing is similarly complicated like the hires screen. Here is
a table with the starting addresses of the lines (left side of the
screen):

line  0 : $0400
line  1 : $0480
line  2 : $0500
line  3 : $0580
line  4 : $0600
line  5 : $0680
line  6 : $0700
line  7 : $0780
line  8 : $0428
line  9 : $04a8
line 10 : $0528
line 11 : $05a8
line 12 : $0628
line 13 : $06a8
line 14 : $0728
line 15 : $07a8
line 16 : $0450
line 17 : $04d0
line 18 : $0550
line 19 : $05d0
line 20 : $0650
line 21 : $06d0
line 22 : $0750
line 23 : $07d0


Important:

Naturally these adresses don't fill the 1K-memory area as the screen is
only 960 bytes large. The unused areas are called "screen holes" and
are used for certain hardware registers (serial interface cards, mouse
card, 80 column hardware, Apple IIc memory control) - so don't change
them unless you know exactly know what you do!

bye
Marcus