The display device is a read/write device with a handler that supports the following CIO functions:
OPEN CLOSE GET CHARACTERS GET RECORD PUT CHARACTERS PUT RECORD GET STATUS (null function) DRAW FILL
The Display Handler can produce the following error statuses:
$84 -- Invalid special command. $8D -- Cursor out-of-range. $91 -- Screen mode > 11. $93 -- Not enough memory for screen mode selected.
The Display Handler is one of the resident handlers and therefore has a set of device vectors starting at location E410.
You can operate the display screen in any of 20 configurations (modes 1 through 8, with or without split screen; plus mode 0, and modes 9 through 11 without split screen). Mode 0 is the text displaying mode. Modes 1 through 11 are all graphics modes (although modes 2 and 3 do display a subset of the ATASCII character set). Modes 9 through 11 require a GTIA chip to be installed in place at the standard CTIA chip.
In text mode 0 the screen is comprised of 24 lines of 40 characters pet line. Program alterable left and right margins limit the display area. They default to 2 and 39 (of a possible 0 and 39).
