Chapter 2 of De Re Atari: ANTIC AND THE DISPLAY LIST. Retrocomputing podcast about the Atari 8-bit line of personal computers. Vol. 1 – No. 1. Antic issue Vol. 1 – No. 1. April – (PDF). Vol. 1 – No. 2. Antic issue Vol. 1 – No. 2. June – (PDF). Vol. 1 – No. 3. Antic issue Vol. 1 – No. 3.
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Antic Atari magazine scans, pdf
This does not mean that 1. One simple application of display list modifications is to vertically space lines on the screen by inserting blank line bytes. For this reason atrai picture that the computer puts out must be somewhat smaller than the television can theoretically display.
Because the screen memory can be accessed by two pointers and relocated anywhere in available memory, it is extremely easy to implement hardware scrolling and page flipping to enable easy game design and programming. Go to the sample graph. It then turns back on and sweeps across the screen antoc. It may sometimes be necessary to use a second LMS instruction. It will begin fetching display data from this area. ANTIC generates displays by executing these display list instructions.
The most common example is changing the background color. The display list terminates with a JVB instruction. So, where Horizontal scrolling is implemented, vertical scrolling is also supported just atrai changing the value incrementing or decrementing the LMS addresses.
See also Software-driven graphics modes for the Atxri 8-bit computers. Blank Mode lines cannot be contained within a scrolling region, because Blank Mode line instructions inherently do not have Fine Scrolling Modifier bits. The Display Lists for these displays require the LMS option added to a Mode instruction near the middle of the display where screen memory crosses the 4K boundary.
This instruction is normally used to terminate a display list by jumping back up to the top of the display list. Now if the display list tells ANTIC to first plot a mode 2 row of characters, then two mode 0 rows, then a bunch of graphics 8 blocks, it will do that.
The same technique can be employed to display far more colours than seemingly allowed in any particular graphics mode, which can be mixed and altered at will. Screen memory can be placed anywhere in the address space of the computer. An electron beam is generated at the rear of the television tube and shot toward the television screen.
This is to defeat vertical overscan by bringing the beginning of the display 24 scan lines down. There are many examples of demo programs available on the internet, displaying these and other features.
The Atari display is built as a series of ANTIC instructions each describing a line of text or graphics mode progressively from the top to the bottom of the screen until the desired display area is filled.
By flipping through a sequence of displays cyclic animation can be achieved. Together the two chips provide 6 text and 8 graphics modes 14 total.
ANTIC The Atari 8-bit Podcast
When the scrolling region of a display requires multiple LMS address updates the possibility of a partial update increases, and the possibility of having two subsequent lines display the same data also increases. Star Raiders, Solaris and Pokey”. Second, if you wish to use any of the operating system antoc routines you must abide by the conventions the OS uses.
For more detailed descriptions of each Mode see the Playfield Graphics Modes section. antuc
The video hardware is constantly dipping into this RAM area, getting screen data that it converts into television signals. Blank line instructions produce blank lines with solid background color. Changes to registers outside of proper time windows may result in delayed effect or unexpected results.
ANTIC buffers the first few bytes read from screen memory that are sufficient to cover the 16 color clock range of movement. You can fool the OS into cooperating by poking a different value there. Graphics mode 10 graphics mode Number of colors: Archived from the original on If you can, have an Atari available to try out the examples. It should be possible to produce interesting effects with such lists.
In a standard byte line display, BASIC would position the characters onto the tenth line by skipping bytes from the beginning.
The Atari has so many demands put on it by its graphics abilities that it comes equipped with two processors. Graphics mode 13 text mode Number of colors: The quality of the image that gets to the screen depends on two factors: Likewise, turning off the display is not antiv if the setup occurs during the vertical blank.
Combining the Map and Character Mode instructions with the LMS bit makes it possible to set the screen memory address freely within the 64K address space independently for each display line. Graphics mode 4 graphics mode Number of colors: Moving a kilobyte or more of memory is CPU intensive and slower computers may not be able to accomplish anything else while updating screen data. Of course, there are some drawbacks to this method.
In this way information from all over the address space of the computer can be displayed on a single screen.