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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Thus, atrai normal limit of resolution of a television set used with this computer is pixels vertically. There are six character display modes. The LMS instruction is a 3-byte instruction: The end result is a Mode F display where the lines are four scan lines tall rather than one, but with the DMA overhead of only one screen memory data read occurring on the first scan line.
ANTIC The Atari 8-bit Podcast
There are 24 display blocks being shown on the screen in Graphics 0. The standard unit of horizontal distance is the “color clock. The processor gets its data and instructions from memory, does its processing, and places data back atnic memory. Naturally, that trivial example is of limited usefulness.
Note that this means that display data anhic not fully relocatable. The display list and the display data are written into RAM by the See the Limitations section. The Apple video hardware is smart enough to interpret a screen memory byte as either an 8-bit character text modetwo 4-bit color nybbles lo-resolution modeor 7 individual bits for a bit map hi-resolution mode.
The 4K boundary cannot be antid within the middle of a Graphics Mode line, but only between the end of one Mode line and the beginning of the next line. It is the responsibility of the DLI routine to save the state of the registers used during the DLI, and then restore the original values of the registers before exiting with an RTI instruction.
ANTIC lives to do display work only, and, like theis a microprocessor. One of them is mixing graphics modes on the screen. A graphics 0 display is one row of characters. In double line resolution the first and last four bytes are ignored, in single line resolution the first and last eight bytes.
Views Read Edit View history. Since it can be located anywhere in the memory, there is little difficulty finding a sufficiently sized place in memory aari does not cross a 1K boundary.
Most display lists are less than bytes long. Then it starts the cycle all over xntic. So, the display is actually a view port that is moved to look at a different areas of memory rather than moving the memory into a fixed screen map.
Antic Software – Wikipedia
ANTIC has an instruction in its display list which keeps it waiting until the time rolls around for a new screen refresh every sixtieth of a second. The period during which the beam returns from the right edge to the left edge is called the “horizontal blank. If you absolutely must have it cross such a boundary, insert a JMP instruction just in front of the boundary.
Then follows the display list proper, which lists the display bytes for the mode lines on the screen. ANTIC is a true microprocessor; it has an instruction set, a program, and data. As HSCROL increases more color clocks from the end right side of the buffered data are added to the left edge of the display causing the fine scroll shift to move the screen contents to the right.
The fundamental problem any microcomputer has in using a raster scan television for display purposes is that the atqri display is a dynamic process; because of this, the television does not remember the image.
The handles all the usual computer processing; executing Basic programs, writing data to atar, and so arari. This is a display list which the changes during vertical blank periods. It will, and the display will pop up on the TV. Only the lowest 4 bits are significant. In this way information from all over the address space of the computer can be displayed on a single screen.
The usual purpose is to change display-related values at a known location so transitions are visually precise or occur angic they will not conflict with display activity. This powerful design allows the Atari qntic computers to produce complex, mixed-mode displays without direct CPU intervention while other platforms, even those designed much later, cannot either mix graphics modes in one display, or do so without direct, complex CPU interrupts.
The display list system can be used to produce appealing screen displays. The total number of horizontal scan lines produced by the display list should always be or less; ANTIC does not maintain the screen timing requirements of the television.
While the usual operation of the DLI is to change a few display-oriented values, and then return to the main code, this is not a requirement. This is done by writing machine language routines to change the values of hardware registers at different vertical positions on the screen.
This can be of value in setting up independent text windows. Often you must fool the OS to make such displays work. These instructions load the full bits of address, so can atxri used to circumvent the 1K Display List limitation.