MOS Technology 8568

The MOS Technology 8568 Video Display Controller (VDC) was the graphics processor responsible for the 80 column or RGBI display on D[CR] models of the Commodore 128 personal computer. In the Commodore 128 service manual, this part was referred to as the "80 column CRT controller." The 8568 embodied many of the features of the older 6545E monochrome CRT controller plus RGBI color.

The original ("flat") Commodore 128 used the 8563 video controller to generate the 80 column display. The 8568 was essentially an updated version of the 8563, combining the latter's functionality with glue logic that had been implemented by discrete components in physical proximity to the 8563. Unlike the 8563, the 8568 included an unused (in the C-128) active low interrupt request line (/INTR), which was asserted when the "ready" bit in the 8568's status register changed from 0 to 1. Reading the control register would automatically deassert /INTR. Owing to differences in pin assignments and circuit interfacing, the 8563 and 8568 are not electrically interchangeable.

The Commodore 128 had two video display modes, which were usually used singularly, but could be used simultaneously if the computer was connected to two compatible video monitors. The VIC-II chip, also found in the Commodore 64, was mapped directly into main memory—the video memory and CPUs (the 8502 and Z80A processors) shared a common 128 KB RAM, and the VIC-II control registers were accessed as memory locations (that is, they were memory mapped).

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