Atari 400

CHACTL (Character Control)(D401): This address writes data into the
Character Control Register.
Not
Used
D2 D1 DO
D2 Character Vertical Reflect Bit. This bit is sampled at the
beginning of each line of characters. If true it causes the
line of characters to reflect (invert) vertically (for upside
down characters).
D1 Character Video Invert Flag (used for 40 Character Mode
only). If bit 7 of character code is true this flag causes
that character to be blue on white (if normal colors are
white on blue).
DO Character Blank (Blink) Flag (used for 40 Character Mode
only). If bit 7 of character code is true this flag causes
that character to blank. Blinking characters are produced by
setting bit 7 of the characters to 1, then periodically
changing DO of CHACTL.
OS SHADOW: CHACT (2F3)
DLISTL(
Display List Low )(D402): This address writes data into the
low byte of the Display List Counter.
D7 D6 D5 D4 D3 D2 D1 DO
Display
7 6 5 4 3 2 1 0
List
Counter
Bit
OS SHADOW:
SDLSTL (hex 230) Position.
DLISTH (Display List High)(D403): This address writes data into the
high byte of the Display List Counter.
D7
D6 D5 D4 D3 D2
D1 DO
~Display
15 14 13 12 11 10 9
8 List
Counter
Bit
Position.
OS
SHADOW: SDLSTH (HEX 231)
The
Display List is a list of display instructions in memory. These
instructions are addressed by the Display List Counter. Loading these
registers defines the address of the beginning of the Display List. (See
sections I and II.)
Note: The top 6 bits are latches only and have no count capability, therefore
the display list can not cross a lK byte memory boundary unless a jump
instruction is used.
III.5