MOS Technology 8563
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The MOS Technology 8563 aka VDC (for Video Display Controller) was MOS' 80-column RGB display video chip used in the Commodore 128 home computer (the C128 also had a VIC-II for producing bitmap graphics and 40-column text, and for C64 compatibility).
History and characteristics
Originally intended for a planned (but unreleased) UNIX-based business computer, Commodore designed the 8563 into several prototype machines, of which the C128 was the only one to be completed, industrialized, and released. The 8563 was a departure from other MOS video chip designs in that it had its own dedicated memory, and memory space, separate from system memory. In addition, yields on the chip were very low, and Commodore's official position after the release of the C128 was that the VDC was incapable of producing bitmapped graphics.
Usable bitmap modes were nevertheless discovered within a year of the C128's release; an extension to the C128's BASIC 7.0 that enabled these capabilities appeared in RUN, a magazine dedicated to Commodore 8-bit computers. This extension would later be refined into the commercially available BASIC 8 for the C128. The various graphics modes were later documented in the Commodore 128 Programmer's Reference Guide as well (reference information: see the C128 article), and the bitmap modes were the basis of the C128 variant of the GEOS operating system.
Although the VDC did have usable high-resolution graphics modes, it lacked hardware sprite capabilities, which limited the C128's use as a gaming platform in its own right.
Data transfer, programming
Programming the 8563 was done by writing to the chip's memory mapped address register (main memory location $D600 = 54784) and then to its data register ($D601), whereupon the data would be written to the addressed internal 8563 control register. There were a total of 37 registers, of which one was the internal data register used for writing to the VDC's RAM* (16KB in the C128 and original plastic cased C128D, 64KB in the later metal cased C128D, also known as C128DCR). Addressing the RAM was done via other registers, such as no.s 18, 19 (Update Address HI, LO). There were also registers for smooth scrolling and light pen handling.
(* In cases where the C128's 80-column mode didn't have to be used, or no RGB monitor was available, the 8563's RAM could be used as extra memory for storing ordinary program code or data.)
Technical specifications
- 16 or 64 KB address space for screen, character and color memory (dedicated, separate from system memory)
- 640 × 200 pixel video resolution (640 × 400 in interlaced mode)
- 80 × 25, 80 × 50, 40 × 25 characters text resolution
- 16 colors
| List of 65xx(x)-based products from MOS Technology and the Western Design Center |
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Single board computers (kits), and microprocessors: MOS/CBM KIM-1 |
6501 |
6502 |
65C02 |
6507 |
6508 |
6509 |
6510/7501/8500-01 |
8502 |
65802 |
65816 Support chips: 6520 PIA | 6522 VIA | 6526 CIA | 6529 SPIA | 6530 RRIOT | 6532 RIOT | 6551 ACIA | 6560 VIC | 6567 VIC-II | 6581 SID | 6845 | 7360 TED | 8563 VDC |