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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There are dots on scan lines, individually refreshed 60 times a second; X X 60 is 3.
Archived from the ztari on It is not a processor, but a smart custom chip only found in the Atari. The effect of vertical “fine” scrolling for single scan line Map modes can be performed using the easier coarse scrolling method.
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One of them is mixing graphics modes on the screen. So, where Horizontal scrolling is implemented, vertical scrolling is also supported just by changing the value incrementing or decrementing the LMS addresses.
ANTIC is in charge of memory control. The main processor of the Atari is called a Blank Mode lines cannot be contained within a scrolling region, because Blank Mode line instructions inherently do not have Fine Scrolling Abtic bits.
As a means of animating a display the results can be jerky when the CPU cannot update the screen memory faster than the display hardware reads the memory to generate the video output. Horizontal scrolling requires the same Display List implementation as the worst case example described for Vertical Coarse Scrolling.
In any case, this is easy to avoid, since this is not a practical Display List arrangement as this places the Mode line in the overscan area where it is not ordinarily visible. Dan B’s Home Page. GTIA also adds some factors of atarl own, such as color values, player-missile graphics, and collision detection.
Graphics mode 6 graphics mode Number of colors: The quality of the image that gets to the screen depends on two factors: In simple display lists the LMS instruction is used only once, at the beginning of the display list.
However, a Qtari Mode instruction can be used to end atqri scrolling region and is still subject to the expected scan line height changes per the vertical scroll value. As the cursor is moved vertically, the display list is changed. It will, and the display will pop up on the TV. Dot Graphics Line Next Section: Blank lines are also useful for partitioning parts of a custom display with different purposes i. For more detailed descriptions of each Mode see the Playfield Graphics Modes section.
Since the DLI is machine code executed by the CPU, any kind of processing work is possible provided it is short enough to not conflict with other activity and atxri not overrun a subsequent Display List Interrupt. A display list should not be built with a hi-res Mode F instruction in scan line —the last displayable scan line. The GTIA Map modes must be horizontally scrolled in steps the size of an entire pixel 2 color clocksinstead of one color clock.
ANTIC The Atari 8-bit Podcast
We design our displays around the available scan lines. When the fine scrolling limit is reached, scrolling continues by resetting the VSCROL value and performing a coarse vertical scroll of the scrolling region. Do not limit your imagination to this pattern; with the display list you can create any sequence of mode lines down the screen. Horizontal coarse scrolling requires a little more effort than vertical scrolling. Video Inverse and Video Blank enabled together result in reverse video characters displayed as an inverse blank space.
Since characters are 8 scan lines high, the display block height is 8 scan lines.
A final suggestion concerns a subject that is laden with opportunities but little understood as yet: It then turns back on and sweeps across the screen again. If you store 41 bytes of data for a mode 0 line, it will not wrap around. The JMP instruction’s operand is antlc address of the first byte on the other side of the boundary.
Vertical scrolling on this display requires updating one LMS modifier address for each Mode line in the scrolling region. Second, if you wish to use any of the operating system screen routines you must abide by the conventions the OS uses. If we were in graphics 8, ANTIC would have to look to the display list times, and find a graphics 8 instruction that same number of times. For this reason most microcomputers have special hardware circuits that handle the television.
At the bottom of the screen after the nd line is drawnthe electron beam is turned off and returned to the upper left corner of the screen. It is achieved by moving bytes of memory through a designated screen display area. These modes use combinations of mixed display lists, scrolling, page flipping, and Display List Interrupts to achieve displays with alternate resolution and increased color that are not possible using the hardware alone.
This makes a load memory scan command. Video Reflect is useful for situations requiring mirroring effects without defining a new character set. Changes to registers outside of proper time windows may result in delayed effect or unexpected results.