This Retro ISA Card Emulates Old Video Standards

If you have been using PCs since the 1980s, then you have enjoyed working on the IBM PC monochrome graphics adapter (MDA) and the IBM color graphics adapter (CGA). Tube Time has developed a retro-style ISA video card emulator that supports these video standards.

In today’s world it is not very difficult to find graphics adapters, so why do you need an emulator for old video standards? Tube Time explains that modern LCD monitors are difficult to sync with unusual frequencies used by MDA (18KHz) and CGA (15KHz). So, the Graphics Gremlin video cards are designed to interface with a VGA port to deliver video running at standard (31KHz) frequency, making it easy to operate on any modern LCD screens.

“The logic is defined by the bitstream loaded into the FPGA, new emulations may be available in the future to support other video standards,” the designer writes. To program the PCB, Tube Time used an FTDI FT2232H Mini module for which the wiring is provided in the GitHub repository. The FPGA code upload is done using the Verilog language, which is divided into two parts — one for CGA graphics and another for MDA graphics. After powering the board, you can upload the code on flash memory through the Project IceStorm tool.

The red switch on the PCB is used for controlling the bitstream selected by the FPGA and specific settings for the chosen bitstream. This is programmed according to your ease, the table for this is also available in the GitHub repo. However, after the project, Tube Time notes that “the VRAM interface is specific to the 8-bit SRAM chip that I am using instead of the 16-bit SRAM on the original MDA or the 16-bit DRAM used on the CGA, so it had to be quite different from the originals.”

Moving forward, we wouldn’t be surprised to see support for more video standards, including EGA and VGA.