Dan Mons

Graphics Gremlin – open source MDA/CGA ISA video card

Tube Time has announced via their Twitter feed the availability of a new, open source graphics card for PC compatible computers with an 8-bit ISA BUS, named “Graphics Gremlin”.

The card is designed entirely with new components, and driven by an FPGA. It can connect to an PC compatible computer with an 8-bit ISA bus, and currently emulates IBM PC MDA (Monochrome Graphics Adaptor) and IBM CGA (Color Graphics Adaptor). This standard was very common during early CP/M, PC-DOS and MS-DOS era personal computers such as the IBM PC, XT, AT and their numerous clones, just before EGA and VGA graphics standards became popular.  Video cards for this era of computing are becoming much more difficult to find, and an open source, newly available replacement is very welcome.

Originally these MDA and CGA video standards were sent to low resolution, compatible CRT screens via 15KHz or 18KHz signals over a DB9 connector, which the Graphics Gremlin supports.  However, this new card also supports 31KHz video modes over a modern VGA DE15 connector, for easy connectivity to modern VGA CRTs, compatible TVs that support analogue VGA, VGA compatible video capture devices, or devices like the OSSC.

Tube Time mentions that they won’t be mass-producing the device, instead releasing the entire project, including KiCad compatible PCB files, schematic libraries and Verilog source files, to GitHub, under a Creative Commons Attribution-ShareAlike 4.0 International License.  They also note that there’s potential to extend the functionality beyond MDA/CGA graphics, courtesy of the on board FPGA.


If you’re a fan of vintage electronics in general, Tube Time‘s website and Twitter feed are also both worth a read and a follow.  The regularly post all sorts of fascinating information about vintage components, including many cross sections and extreme close up photography of all sorts of components and equipment.

Twitter feed: https://twitter.com/TubeTimeUS

Website: http://tubetime.us/