BX-Plorer: Meet the New Card, Same as the Old Card

A project log for VDC-II

Commodore 8568-inspired (and mostly compatible) video core for driving VGA-type displays.

Samuel A. Falvo IISamuel A. Falvo II 10/08/2020 at 20:110 Comments

As this project evolves, I'm noticing a distinct yet synergistic compartmentalization in the roles and responsibilities of different project components.  When I started this VDC-II project, I'd just been convinced by interested members of the community of the value of developing Kestrel-3 computer parts for the RC2014 backplane.  I later observed that my RC2014 Zed's flash BIOS image could be built with Commodore VDC support, and after reading up on that chip's technical specs, I realized that it was a fairly close match to what I'd wanted to achieve with my own CGIA concept.  So, rather than re-inventing the video support with the CGIA, I figured I'd just piggy-back what was already there, and decided to reimplement the VDC.  This benefits both RC2014 and Kestrel-3 communities, since any Kestrel-specific enhancements I make to the design later on can benefit both communities, not just the one.  So, I set out to just develop a (mostly but not completely compatible) clone of the Commodore 8563 VDC as used in the Commodore 128, using affordably priced, off the shelf FPGA development boards.  That became the VDC-II project you're reading about now.

I've always intended to release this project as a kit of some kind, so that RC2014 owners can, in long-standing RC2014 community tradition, build their own video card.  That means, as part of the kit, they'd receive the PCB, all the chips, a pre-programmed TinyFPGA BX module, and other miscellaneous parts needed to have a working video card.

However, I now realize that the very circuit I used to interface my TinyFPGA BX module to the RC2014 backplane is itself useful as a self-standing product in its own right.  You could see a less developed realization of this, more or less explicitly, in previous log entries where I first mention breaking up the FPGA part of the circuit from a mezzanine card containing the analog VGA circuit.

Going forward, I've decided to formalize the separation of the FPGA project card from its applications.  First, the FPGA project card now has an official name: BX-Plorer.  It lets the consumer of the card explore FPGA designs using the TinyFPGA BX module.

Second, I've decided to factor the BX-Plorer out into a separate git repository.  I'll update my configuration accordingly shortly after making this post.  This implies that, Coming Soon, there'll be a separate Git repository for the VDC-II design files and the software stack needed to drive it.  I'll (re)post updated links in a separate log when everything is in place.

Related to the first two points above, for now, both BX-Plorer and VDC-II updates will happen in this project.  As I write this, I have no plans of factoring the two projects out here.  These two projects have been co-developed from the get-go, and I don't see that changing any time soon.

Third, what of the VDC-II-based RC2014 "video card"?  Is that now dead?  As I'd originally conceived it, yes.  With all the other video card projects that people are concurrently producing for the RC2014 (link 1, link 2, link 3), it's not clear to me how I can compete for mindshare.  However, if there's enough feedback, I can see offering a BX-Plorer Cost Reduced/Fixed Function card as a dedicated video card.  If this is something that is still desirable to readers, please do get in touch to let me know.

(Besides, you can always use a regular BX-Plorer with a pre-programmed TinyFPGA BX and analog VGA mezzanine still.)

Fourth, this does not affect the development of the VDC-II itself.  I still need a video card, for both my RC2014 and for my own future homebrew computer design.  The VDC-II project is not dead.

When, not if, you see these new terms being bandied about in my project updates, now you'll know why and where they come from.  :)  Until next time!