A Dual Monitor Setup For The C64, And Yes, It’s VGA Compatible

Few in the 1980s were too fussed about their home computer only supporting a single monitor; indeed, most were satisfied enough by the brand new capabilities on offer at the time. That said, it’s many decades hence, and we really do deserve more. Fear not, for [Ryan Brooks] is here to help with his VG64 VGA Card for the Commodore 64.

The card sits in the cartridge slot of the Commodore 64, and packs a Xilinx CPLD which is responsible for generating the video output signals. It’s hooked up to an SRAM chip which acts as a frame buffer for the video output. Programs can then be loaded on the Commodore 64 which write to the frame buffer, that can then be sent out to an attached VGA monitor hooked up to the cartridge.

It’s not the most useful cart at the moment, as it’s only capable of working with software designed specifically for the hardware. Additionally, it could prove difficult to shift enough data to it to do any kind of fast animation or updates. With that said, it’s an awesome example of just what can be achieved in terms of expanding the Commodore 64, and we’d love to see how far work in this space can go. We’ve seen similar work before, too, albeit with a somewhat smaller 16×2 character LCD. Video after the break.

9 thoughts on “A Dual Monitor Setup For The C64, And Yes, It’s VGA Compatible

    1. You can “maybe” sort-of do this already. Using a PiStorm (Raspberry Pi-based 68k implementation), originally developed for the Amiga but should in theory work on any 68k-based system, you should be able to effectively get up to 80 MHz. I don’t know if anyone has used this for anything beyond an Amiga though. Oh, and on the Amiga, you can use the Pi’s HDMI output. Maybe one day that could be used for other 68k-based systems as well.

      As for outputting to an LCD, using the RGBtoHDMI project (also Pi-based!), you should be able to get video out (monochrome only of course) via HDMI and hook that up to an LCD panel. Since early Macs used odd refresh rates and timings, the RGBtoHDMI adapter needs to be adjusted, but it’s doable. Adrian’s Digital Basement recently did a video about this using a Macintosh Classic. You could technically also just straight-up capture the composite out and send that to an LCD, but you’d need a way to compensate for the timings, making the RGBtoHDMI a better option.

      3rd party Firmware/ROM’s do exist, though I don’t know if there are open-source options.

      As for an open source OS, I’m sure there are some Linux distros that will work with low-end Macs.

  1. Fun project! Perhaps it could be altered to function as an 80 columns card. Although there isn’t much compatible software for those either, but there should be at least one or two programs / word processors that support 80 col video cards. As these did exist back in the days for these purposes.

    Anyway, compatibility (usability) is often referred to when someone makes something for an old system. But I doubt if this was ever created with that in mind. In many cases it’s just fun to make something with modern components connected to an ancient system. It’s fun to achieving magical things that are only 35 years too late to be really appreciated. Please keep on this good work and keep us posted.

    1. Thanks Jan. There’s no text mode, so 80 columns would be difficult, but certainly a future version could add a lot of capability- including something like this. I will say I’m pleasantly surprised how well the kernal deals with a 80 column screen.

  2. I am pretty sure that in the (later) 80s Apple computers would support as many monitors as you could fit graphics cards. So if you had 8 NuBus slots, you could have 8 monitors.

  3. At first I thought this might be a doubling up of video RAM so graphics mode and text mode can used at the same time to different screens but most retro systems didn’t a hardware based text mode as character generator ROMs are too slow.

    It all looks good, though it’s getting a bit sluggish. Even 320×240 4bpp is a bit much for and old slow CPU.

    Interesting that he used an Xilinx XL95144XC 144 macrocell CPLD, probably could have used a 72 macrocell but perhaps he needed the extra I/O.

    A lower res mode would good as the CPU could update much faster. Also a 6845 like setup could be good for scrolling games. He may have the spare gates in the CPLD to do that.

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