5150: Setting up MDA/CGA (without having an IBM monitor available)


Old monitors do wear out and they are difficult to build (lots of glass, a CRT, and intricate components). So it is much more practical to adapt old video signals into more modern display devices.

The original MDA and/or CGA video cards of the IBM PC use a 9-pin connector. More modern VGA monitors use a 15-pin connector. So be aware that “VGA” can refer to both a set of 256-color video modes, and “VGA” can also refer to the type of cable connection. So the meaning will depend on the context of how it is used.

VGA as a connection style is largely phased out, now with DVI, HDMI, and DisplayPort connectors (which support even higher resolutions of video). Adapting the legacy MDA/CGA signals to a VGA monitor is not an easy process, so don’t expect an inexpensive $10 dongle-type adapter. Instead you will need to find a powered adapter, such as one of the following:

I do prefer the MonoTech since the buttons and dip-switches are more apparent and labeled on its case. But the texElec version I received may be a little easier to mount onto an electronics project board.

These are “made-to-order” devices that may be built in limited-run batches. They aren’t massed produced in a factory. The PCB spec is generally available online (github). So don’t be disappointed if they take awhile to order, and appreciate that they may have been hand built by someone just for you.

These devices won’t come with a VGA cable, so you will need that as well, and a CRT or LCD that has a VGA input. They might come with an MDA cable, double check during the order. If you want to adapt to an even more modern HDMI or DisplayPort, then an additional adapter will be needed. Some televisions may have a VGA input.

Below is the CGA/MDA card that I have. Note it has a parallel port and also a Composite Video out.

Notice how both connectors at the back of this video card are 9-pin. Both MDA and CGA were 9-pin connectors. This particular video card can only do one at a time (but you can switch without rebooting or adjusting any pins on the motherboard).

The IBM standard put the monochrome and color outputs at different addresses, so one could have both an MDA video card and CGA video card independently output two separate monitors. Often what I did was to have a TSR (Terminate Stay Resident) background program to output the current time (as well have an alarm clock feature) to the MDA screen, while doing the more typical programs and applications on the color monitor.

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