Atari 400 Hardware Manual

Xixing Graphics Xodes, cont.
III. PROCEDURE T0 PRI~T AND PLOT IN MIXED MO~ES, cont.
2. Some modes may have mode line #'s outside of their normal
range.
example:
~ ~ de 2 normaljy has mode line #'s 1 through 12
(full screen). Th ~ se are modif ' ed to #63 and
#64 in exaruple #1.
To prevent the computer from giving a "cursor out of range"
error message the following procedure can be used:
a. Set a variable labelled "MEMST" to be the display
memory start pointer.
~EMST = PEEK(START) + PEEK(START + 1) * 256
b. Set a variable labelled CHRPOS to position characters
to be printed on the target line.
CHRPOS = ~1EMST + [(Ml-1)*R-~
2
*(R-20)-~
3
*(R-10)]+X
Hhere:
X = horizontal position of character on the target
line.
R the RAX per line of the Max RAM Mode (table #1).
M
1
= the Mode Line If of the target 1 in e.
M
2
= the number of mode lines of 20 bytes of RAM per
line above the target line.
~
3
= the number of mode lines of
line above the target line.
10 bytes of RAM per
Example: calculate CHRPO~ for Mode Line #64 (the
last line of the Mode 2 area) at horizontal
position 5.
X 5
R 40
M
1
6 4
M
2
7 (6 from Mode 1 area, 1 from Mode 2 area).
M
3
0
CHRPOS
CHRPOS
CHRPOS
CHRPOS
CHRPOS
=
~EMST
+
HEMST
+
MEMST
+
MEMST
+
MEMST
+
[(64-1)*40-7*(40-20)-0*(40-10)]+5
[ (63) *40-7* (20)-0* (30) J +5
[2520
-
14 0 J
+
5
[2380] + 5
2385
B -6-
-

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)