Mode 8/Mode 9 Horizontal Scroll Corruption
ANTIC Modes 8 and 9 will be corrupted when immediately following a horizontally scrolled line of a different mode using normal or wide playfield width. This occurs if the Mode 8 or 9 line is horizontally scrolled or not, but the corruption results are different in each case. The problem appears for certain HSCROL values causing ANTIC to output pixels incorrectly and mis-align the Mode 8-9 line.
Note that the bug does not occur when narrow width playfield is used.
- If Mode 8 or 9 is NOT using Horizontal scrolling and follows:
- Mode 2, 3, 4, 5, D, E, or F and HSCROL is $A, $B, $E, or $F: then corruption continues through the mode line.
- Mode 2, 3, 4, 5, D, E, or F and HSCROL is $C or $D: then corruption resolves itself within two scan lines.
- Mode 6, 7, A, B, or C and HSCROL is $E or $F: then corruption continues through the mode line.
- If Mode 8 or 9 is using Horizontal scrolling and follows:
- Mode 2, 3, 4, 5, D, E, or F: then corruption resolves itself within three scan lines.
- Mode 6, 7, A, B, or C: then corruption resolves itself within two scan lines.
Since the HSCROL values causing the problem are greater than 7, the problem can be averted when Mode 8 or 9 is NOT using Horizontal scrolling by limiting HSCROL shifts to 0 through 7 color clocks and updating the Display List LMS address to horizontally coarse scroll in smaller increments. This strategy resolves all cases in all the Text modes, and all Map modes from A through F which generate 8 or fewer color clocks per byte of screen memory.
Read more about this topic: ANTIC, Bugs and Border Conditions, Unexploitable Behaviors
Famous quotes containing the words mode, horizontal, scroll and/or corruption:
“The mode of clearing and planting is to fell the trees, and burn once what will burn, then cut them up into suitable lengths, roll into heaps, and burn again; then, with a hoe, plant potatoes where you can come at the ground between the stumps and charred logs; for a first crop the ashes suffice for manure, and no hoeing being necessary the first year. In the fall, cut, roll, and burn again, and so on, till the land is cleared; and soon it is ready for grain, and to be laid down.”
—Henry David Thoreau (1817–1862)
“And yet out of eternity, a thread
separates itself on the blackness,
a horizontal thread
that fumes a little with pallor upon the dark.”
—D.H. (David Herbert)
“I am the scroll of the poet behind which samurai swords are being sharpened.”
—Lester Cole, U.S. screenwriter, Nathaniel Curtis, and Frank Lloyd. Prince Tatsugi (Frank Puglia)
““Our earth is degenerate in these latter days. Bribery and corruption are common. Children no longer obey their parents. . . . The end of the world is evidently approaching.” Sound familiar? It is, in fact, the lament of a scribe in one of the earliest inscriptions to be unearthed in Mesopotamia, where Western civilization was born.”
—C. John Sommerville (20th century)