Romain Dolbeau's NuBus Card Brings a Modern FPGA, HDMI, and VGA to Classic Apple Macs

Retrocomputing enthusiast Romain Dolbeau has launched a project that aims to interface a modern field-programmable gate array (FPGA) with classic Macintosh II and Macintosh Quadra systems via the NuBus — and has already succeeded in giving the hardware a modern HDMI-compatible output.

"I've been thinking about rolling my own NuBus display board, based on the same idea as a previous project of mine: The SBusFPGA, an expansion board for my 90s SPARCstations," Dolbeau explained of the project when first proposing it in December last year. "Basically I would just do a NuBus-compliant carrier board with an existing FPGA daughterboard (reusing the same daughterboard as for the SBusFPGA), with just level shifters and I/O interfaces on the carrier."

This week, Dolbeau issued "a significant update" to the effort: a fully-functioning prototype, which adds HDMI and VGA compatible video outputs to vintage Macintosh systems. "As of earlier today, the board will pass POST in my Quadra 650," Dolbeau announced, "and the embedded declaration ROM (in the FPGA bitstream) will enable a single-resolution, 8-bits depth only framebuffer of the desired resolution up to 1920x1080, which is what I'm testing it with.

"This framebuffer will work as a secondary screen, the 'startup' screen (by moving the smiling mac in the Monitor control panel) or as the only screen by unplugging the monitor from the onboard video of the Q650. The framebuffer in the FPGA should be able to support 1/2/4/8 bits and even full color."

There are a few caveats to the project, however — beginning with the fact that it's what Dolbeau describes as "an expensive toy and nothing more." The cards are wider than a true NuBus card, blocking the neighboring slot, the resulting video output is "noticeably slower than the [Quadra 650] internal video," and there's no acceleration.

"They are not easy to make," Dolbeau adds. "The PCB is only four layers but plenty of surface-mount chips including the large Xilinx CPLD [Complex Programmable Logic Device]. They are not easy to set up. The FPGA is simple enough, but the CPLD requires configuration via a dedicated JTAG programmer (which adds to the cost), and Xilinx tools have not been upgraded for years."

For those interested in trying their hand at the project anyway, Dolbeau has a thread running on the 68kMLA forum and has published design files and source code to GitHub under an unspecified open-source license.