Add support for VDC / 80 columns on Commodore 128

[spotlessmind1975]

It is asked to support to the VDC, that provides an 80-column color display (also called RGBI for red-green-blue plus intensity). In 80-column mode the VDC provide blinking and underlined text, activated through escape codes, in addition to the standard Commodore reverse text. The 40- and 80-column modes are independent and both can be active at the same time. A programmer with both a composite and RGB display can use one of the screens as a "scratchpad" or for rudimentary multiple buffer support.

[odflor]

I can imaginate some more uses for a 80 columns display :).

[spotlessmind1975]

Hi @odflor and thank you for the feedback!

The c128z target, which is under development, accesses the VDC by default, both in textual and graphical (bitmap) mode. However, the possibility of using both video chips (VDC / VIC-II) simultaneously is under study, and is part of the integration.

It will probably be necessary to think of a new set of targets, something like this;

• c128 for MOS VIC-II under MOS 8502;
• c128b for MOS VDC under MOS 8502;
• c128c for MOS VIC-II + MOS VDC under MOS 8502;
• c128d for MOS VIC-II under Zilog Z80;
• c128z for MOS VDC under Zilog Z80;
• c128e for MOS VIC-II + MOS VDC under Zilog Z80;

Thank you again and happy retrocoding!

[odflor]

To simplify it could only define c128c and c128e, both with support for the two screens.

But when use only one screen is possible to use the memory of the unused screen as swap memory or similar.