Opening the borders

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The VIC-II draws a border around the C64’s screen and will not let you put anything in it. Opening the borders defeats that by changing the screen-height or screen-width setting at the moment the chip checks whether to start drawing the border — so the check fails, and the border never begins.

Two borders, two problems

Border	First recorded	Date
Top and bottom	Flash/FCG, Intro	11 October 1985
Sides	TSI/1001, Border Letter I	April 1986

The side borders took six months longer because they must be reopened on every raster line, not once per frame. Border Letter I is named for the trick it exists to show.

The priority question the scene gave up on

⚠ This is the dispute the record-keepers use as their example of an unresolvable one. The world-firsts page, explaining why it lists multiple claimants rather than one winner, reaches for this technique specifically:

some of these issues are subject to dispute (for example who was really the first to open the borders?)

Its standing instruction to editors is “in cases of dispute, please do not just list one release as being THE first”. Even the 1985 entry above carries an open question against it — “Is this the one?”

Opening it is not the same as using it

The published sideborder routine is explicit that it only proves the point:

Here is an ugly piece of code that shows how to remove the sideborder. Of course there is much more to desire if you want to use it in a demo, you probably want sprites and perhaps graphics in the open area as well. This just shows how it worx.

Getting sprites out there is a separate exercise, with its own worked example by Groepaz. And the routine has to branch on region — “Fix PAL, otherwise NTSC” — because the timing differs between television standards.

See also

• Stable raster — what the per-line version needs
• Sprites
• Raster interrupts