I have a 486 (also another 286 mainboard) with a Hercules card, the plug is the same as RS-232. Is it possible to connect the output with serial port USB adapter and simulate Hercules-compatible monochrome display on a modern PC?

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    Welcome to Retrocomputing Stack Exchange. I recommend that you read the tour, just so you know how the site works (e.g. you shouldn't post follow-up questions as answers). I would expect that you wouldn't be able to do this purely in hardware, but you would almost definitely be able to create an adapter with an Arduino or a custom hardware board with programmable logic.
    – wizzwizz4
    Nov 26, 2016 at 13:49

4 Answers 4


Unfortunately, Hercules plug, while being the same DE-9 plug/socket as "small" RS232, is completely electrically incompatible - other than using the same connector type, there is absolutely nothing in common between the two interfaces. You can damage the card, monitor or RS232 port/converter if you try connecting RS232 with the Hercules port.

So, no, neither USB-to-RS232 converter, nor genuine RS232 is going to help you here.

I don't know what you can do to create a display for your 486 (other than getting an ISA VGA card in place of your Hercules), but RS232 is definitely not the way to go about it.


If you mean the original Hercules graphics card (picture further up), it had a video port and a parallel printer port.

Neither can be connected to a RS-232 serial port in a sensible way. And even if you could, there's no way you can simulate a graphics card over an RS-232 connection: The graphics card can be only controlled via the ISA bus.

If you want to simulate a Hercules card on a modern PC, you can do this with emulator software like dosbox.

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    I think the OP is asking about reading the output from the Hercules card on a modern PC, not simulating a graphics card. That is to say, the 486 runs software displaying via the Hercules card, connected somehow to a modern PC which acts as a Hercules monitor. (No doubt possible, but not with a serial-to-USB RS-232 adapter.) Nov 26, 2016 at 17:40
  • @StephenKitt: That wouldn't make much sense. What should be accomplished by by having the modern PC read the image (it can't do much with it except display it), instead of directly connecting it to a monitor? But OP should clarify ... and since, no matter what he wanted, RS-232 doesn't work, it's probably moot, anyway.
    – dirkt
    Nov 27, 2016 at 7:54
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    It makes sense if the OP doesn't have a Hercules monitor, or simply wants to display the Hercules output on a modern screen, or wants to capture the Hercules output... Nov 27, 2016 at 8:26
  • @StephenKitt: I think it's much more likely that the OP just saw the port, thought (wrongly) "oh, it's RS-232, can I do anything with it?", and asked. But as I said, OP should clarify.
    – dirkt
    Nov 27, 2016 at 8:29
  • @dirkt: One could do screen captures of software which only runs on vintage hardware.
    – supercat
    Dec 2, 2016 at 0:29

The Hercules / MDA plug is indeed the same physical as the RS-232 serial port (although 25 pin serial was also used) but the signals are very different. It's absurdly expensive to use this signal for anything these days as the only usage left is industrial but converters and even LCD monitors exist.

At one time, MDA to VGA/DVI boxes existed and I found a product called usb2isa which allowed plugging ISA cards into modern PCs via the USB bus but these seem to be not available any more.


A serial port (let's say 38,400 bits per second), besides being electrically incompatible with Hercules, is far too slow to handle the video bandwidth (720 bits x 348 bits x 50 frames per second = 12,528,000 bits per second).

Hercules is essentially an MDA-compatible monochrome card, and a GBS-8219 converts MDA to 800x600 VGA, so with that all you need is a USB video capture card that supports VGA input. But I think it will be cheaper to connect the GBS-8219 directly to a VGA monitor.

Or a Raspberry Pi supports up to about 14-20 MHz on its GPIO pins, so maybe you can write something to read the Hercules signal and display it on screen, then connect to it from your PC with VNC. Which, by the way, you could do through a USB serial adapter by running a SLIP server on your PC, but that would be silly.

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