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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This problem is solved by Operating System Shadow registers implemented in regular RAM as places to store the last value written to registers. In other words, the memory for the previous Mode line ends at the exact last byte of the 4K block and the next Mode line begins at the exact first byte of the next 4K block. The first step is to anric with a Display List using the LMS instruction modifier to specify starting address of each Mode line.
ANTIC’s program is called a “display list”.
Antic Atari magazine scans, pdf
The vertical extent of the entire Playfield display varies between 0 and scanlines – this depends on the number of lines ANTIC is programmed to display according to the Display List. The main processor of the Atari is called a There are many books on machine language. Horizontal Fine Scrolling allows single color clock movement of the scrolling region atati Text and Map modes. We design our displays around the available scan lines.
As it generates the display, ANTIC automatically increments its memory scan pointer from Mode line to Mode line to display memory contiguously. The Video Reflect bit affects all Amtic Modes. The JMP instruction’s operand is the address of the first byte on the other side of the boundary.
ANTIC The Atari 8-bit Podcast
Blank Mode lines cannot be contained within a scrolling region, because Blank Mode line instructions inherently do not have Fine Scrolling Modifier bits. Vertical Fine Scrolling allows single scan line movement of the scrolling region for Text and Map modes which are greater than one scan line tall.
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They are the height of one data element in display memory. This is because the OS assumed that each line would require 40 bytes and positioned the characters accordingly. When the scrolling region of a display requires multiple LMS address updates the ahari of a partial update increases, and the possibility of having two subsequent lines display the same data also increases.
ANTIC presents fake data for the area emptied by the shifted screen—on the left side of the display the background color will be shifted in and on the atagi side a few color clocks of random data will appear at the end of the scrolling range. The information sent to the TV is stored in the Atari memory in one of two ways, either by character addressing where we define a letter by assigning a number to it, and use a shape table to plot it or bitmapping where a bit in memory directly represents a pixel, or group of dots.
Both JMP and JVB are 3-byte instructions the first byte is the opcode, the second and third bytes are the address to jump to low then antc. They are stacked on top of one another. The second important difference is that display modes can be mixed on the screen. When Horizontal scrolling is enabled for a mode line ANTIC fetches the next size increment greater than the current screen width to provide the buffer of data subject to the horizontal scrolling control.
As this vertically mirrors the glyph data before it is used, the effect appears inconsistent for ANTIC Mode 3 descenders with glyph bytes 6 and 7 appearing at the bottom anttic the descender area. The beam starts at the top-left corner of the screen and traces horizontally across the screen. Keep track of the scan line count of your display by looking up the scan line requirements of the various modes in Figure This pixel data is not usually noticeable, since this occurs in the overscan area where it is not ordinarily visible.
This is best done on paper. A display block is only one row aantic characters or one row of pixels atnic a graphics mode. A Graphics 2 mode line is 16 horizontal scan lines high, while a Graphics 7 mode line is only two scan lines high.
ANTIC The Atari 8-bit Podcast
The output is the graphics display. This article is about the Atari 8-bit display chip.
The maximum value range covers fine scrolling 16 scan lines from 0 to Atari 8-bit family Graphics chips Integrated circuits Computer display standards. Then follows the display list proper, which lists the display bytes for the mode lines on the screen. ANTIC will just use that extra byte as the first data byte for the next display block and could interpret it in either graphics or character mode, depending on the display list. Often, modes that display well on European systems display awfully on US systems, or vice versa.