XL/XE Graphics Modes

The new graphics modes are 12, 13, 14, and 15 in BASIC; ANTIC modes 4, 5, 12 ($C), and 14 ($E), respectively. These have always been available internally, but BASIC programmers had to trick the OS to get at them. GRAPHICS 12 is a four-color text mode (plus background). Each character on the screen is the same height as a GRAPHICS 0 charac- ter (8 scan lines), but only four pixels get displayed instead of eight. The screen has 20 lines (24 with GRAPHICS 12 + 16) and 4 lines of text, using 40 bytes of RAM per screen line. GRAPHICS 13 is another four-color text mode (plus background), but this time the characters are double the size of GRAPHICS 0 characters (16 scan lines high), while only four pixels are displayed (the system interprets the character set by bit pairs rather than single bits; see below). The screen has 10 lines (12 with GRAPHICS 13 + 16), also using 40 bytes per screen line. Since both GRAPHICS 12 and 13 display only four bits in each line of character definition, the color of the pixel displayed depends on the bit pair in the byte being addressed: Bit Pair Color RAM Location 00 BAK 712 01 PF0 708 10 PF1 709 11 This depends on bit 7 of the byte. If bit 7 = 0, then use PF2 (at 710), else use PF 3 (at 711). Note that each line in a character set definition (eight lines, one byte wide, form one character) can have different color combinations. Since bit pairs (one color clock) are displayed, the normal character set becomes unrecognizable. In order to use these modes, you should build a character set in which each character is half a letter and can be combined for display. Or build a 7 X 7 character set with a blank row and column between each character. The characters displayed are not the full character set. They are only one half of the ATASCII set, depending on the value in location 756 ($2F4): 224 ($E0) for uppercase, 226 ($E2) for lowercase. When using GET or PUT operations in these modes, the lower seven bits (0-6) are used for character data (allowing a range from 0 to 127; $7F), while the high bit is the color modifier (see the table above). GRAPHICS 14 is a two-color mode with a resolution of 160 pixels wide (half the horizontal distance of GRAPHICS 8) and 192 high (160 with text lines). Each screen line is one scan line high, compared with GRAPHICS 6 where each line is two scan lines (GRAPHICS 14 is sometimes called GRAPHICS 6-1/2). BAK and PF0 are the two-color registers; the first bit of a screen byte identifies the color. GRAPHICS 15 has been made popular by many drawing and paint- ing programs such as Datasoft's Micropainter and both Koala's and Atari's drawing programs for their touch tablets, It is a four-color mode with a resolution of 160 across X 192 down (160 with text lines), each screen line being one scan line high. Colors are BAK, PF0-PF2; only the first two bits of a screen byte identify the byte color. It is sometimes called GRAPHICS 7-1/2. Memory Used ----------- Mode Lines Colors Split Screen Full Screen 12 40 X 20/24 5 1154 1152 13 40 X 10/12 5 664 660 14 160 X 160/192 2 4270 4296 15 160 X 160/192 4 8112 8138 Here are the pinouts on the 800 and XL/XE's monitor jack (looking at the back of the unit): * * * * * * * ******* * * * Audia output * 3 1 * Composite luminance * * * * Composite chroma * 5 4 * Composite video (not available * * on XL models) * 2 * * * Ground

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