Atari 400 Hardware Manual

Mixing Graphics Modes, cont.
II. PROCEDURE TO SET UP SCREEN IN MIXED MODES:
1. Select modes desired, then look up which mode is the max
RAM mode from table #2.
example:
modes selected - mode 1, mode 7, mode 2
mode 7 = max RAM mode
2. Use table #1 to calculate the number of mode lines such
that the total number of scan lines = 192.
example:
scan
lines
II
mode
per scan
mode
line mode
lines
line
1
6
8
48
7 56 2
11 2
2 2
16
32
192
TOTAL
3. If the max RAM mode is at the top of the screen, then skip
this step: Calculate the LMS byte by setting the left
nibble to 4, then use table #1 to find the right nibble for
the graphics mode at the top of the screen.
example:
1. left nibble = 4
2. right nibble for mode 1 6
3. LMS byte = 46 (HEX)
4 •
Calculate the mode byte for each
mode.
Set the left
nibble
to
0'
use table
Ill to
find the right nibble
for each
mode.
example:
I
Left
I
Right!
Hode
Model
Nibble! Nibble!
Byte
I
I I
(HEX)
1 0
6
06
7
0 D OD
2
0
7 07
B -3-

Atari 400 Specifications

General

Manufacturer	Atari
Model	400
Type	Home Computer
Release Year	1979
CPU	MOS Technology 6502
CPU Speed	1.79 MHz
ROM	10 KB
Operating System	Atari OS
Keyboard	Membrane keyboard
RAM	8 KB (expandable to 48 KB)
Graphics	ANTIC and GTIA chips
Sound	4 channels
Display	RF output for connection to TV
Storage	Optional cassette tape drive or floppy disk drive
Ports	Cartridge
Display Resolution	320x192 (16 colors)