MOS Technology 8563

Originally intended for a planned (but unreleased) UNIX-based business computer based around the Zilog Z8000, Commodore designed the VDC into several prototype machines.

Officially, the VDC was a text-only chip, although a careful reading of the technical literature by MOS Technology that was given to the early C128 developers did indicate that a high-resolution bitmap mode was possible—it simply wasn't described in any detail.

BASIC 7.0, the C128's built-in programming language, only supported high-resolution graphics in 40-column mode via the legacy VIC-II chip.

Shortly after the release of the C128 the VDC's bitmap mode was described in considerable detail in the Data Becker book "Commodore 128 - Das große GRAFIK-Buch" (published in late 1985 in the United States by Abacus Software), and an assembly language program was provided by the German authors Klaus Löffelmann and Dieter Vüllers, in which it was possible to set or clear any pixel or, using BASIC to perform the necessary calculations, generate bitmapped geometric shapes on the 80 column screen.

[1] Authors Lou Wallace and David Darus later developed the Ultra Hi-Res utility into a commercial package, BASIC 8.

One of the most popular third-party utilities for the C128, this offered more advanced VDC high-resolution capabilities to a wide audience of programmers.

However, it did contain blitting capabilities to autonomously perform small block memory copies within its dedicated video RAM.

Next the program must wait until the VDC is ready for the access, after which a read or write on the selected internal register may be performed.

Owing to this somewhat cumbersome method of controlling the VDC, the maximum possible frame rate in bitmapped mode is generally too slow for arcade-style action video games, in which bit-intensive manipulation of the display is required.