Joined: Thu May 28, 2009 9:46 pm
Posts: 8155
Location: Midwestern USA
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Spotted on eBay.
The seller has a cache of Commodore 8568 video display controllers (VDC), which were used in the Commodore C-128DCR (the North American version of the C-128D sold in Europe) to generate the 80 column display. The 8568 is a more technically-advanced version of the 8563 VDC used in the "flat" C-128, with relatively faster overall timings, an active low IRQ output and easier interfacing to the rest of the system. As with the 8563, the 8568 can address up to 64KB of video RAM—DRAMs such as 4464 are used. The 8568 handles DRAM refresh...no special circuitry is needed.
If you have a C-128DCR (or a C-128D with an 8568—not all of them did), you might want to consider purchasing one as a backup. Note that the 8568 and 8563 are electrically incompatible—installing an 8568 into a machine with an 8563, or vice versa, will result in a DOA system.
Unlike typical 65xx peripheral hardware, the 8568 makes no reference to Ø2 and when accessing register pairs that set addresses, such as the cursor location, is big-endian. An interesting note is the 8568's IRQ output was not used in the C-128DCR and the device was always operated in polled mode.
I've given some thought to what would be required to adapt an 8568 to a homebrew computer, but am not sure I'd want to be basing a new design on a 36 year old device of which a limited number are available. Also, I'm not aware of the availability of a data sheet for the 8568, so exact timings are, among other things, an unknown. Given the era in which the 8568 was designed (mid-1980s) and the manufacturer (Commodore Semiconductor Group), I think it's safe to assume the device accepts and outputs TTL levels.
The 8568's video output is RGBI, which is the same as what was produced by the video adapters shipped with many of the first-generation IBM PCs. Monitors that support RGBI have gone the way of the dinosaurs, but hardware to convert RGBI to VGA output is available.
_________________ x86? We ain't got no x86. We don't NEED no stinking x86!
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