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I have this monitor, which I think is a Commodore 64 monitor. I would like to connect it to a pc.

Anyone know how to convert VGA or HDMI to this connector format? I've tried searching, but so far I've only found solutions for hooking a C64 up with a VGA monitor, which is kind of the opposite of what I'm aiming for.

Connector Back of screen Front of screen

  • Googling the model number suggests it is an MDA/Hercules monochrome monitor that might have been used with some of Commodore's PC range, but not a 64. Generally you go from MDA or whatever to VGA/HDMI, not the other way around. – bodgit Nov 1 at 9:33
  • See also this very similar question: retrocomputing.stackexchange.com/questions/8551/… – snips-n-snails Nov 1 at 10:51
  • @bodgit Damn. But thanks anyway - if you make that an answer, I'll accept it. – Gertsen Nov 1 at 12:22
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I have this monitor, which I think is a Commodore 64 monitor.

Not really. And especially not for the C64.

The screen was manufactured in Taiwan (*1) for/by Philips. It was widely sold as a monochrome screen to many countries.

What is true is, that Commodore OEMed it ca. 1985 as 1901(*2) or later 75BM13 (*3) for/with the PC10/20/... series (*4) of IBM compatible computers equipped with their AGA card (*3), a CGA / MDA / Hercules compatible adapter.

I would like to connect it to a pc.

It is already a PC one - for MDA cards/output.

That's

  • monochrome at
  • 18.432 kHz with an
  • effective resolution of 720x350 pixels and
  • analogue intensity of
  • 4 levels (used by MDA).

While MDA required 720 pixels at a 16.25 MHz pixel clock (video bandwith) Commodore speced the monitor at 800 and 20 MHz.

The only difference to a standard IBM compatible screen is that a DIN plug is used instead of a DE-9S.

Anyone know how to convert VGA or HDMI to this connector format?

Nope. I bet you would as well not like the loss of information due the downscaling.

I've tried searching, but so far I've only found solutions for hooking a C64 up with a VGA monitor, which is kind of the opposite of what I'm aiming for.

But that's what the usual way is: using older output generators, like a C64, with modern displays.


Now, widening up a bit why not use either an old PC, or if it has to be the new one, why not add an old graphics card to your new PC?

  • There are a large number of USB to ISA boards, ranging from hobbyist projects to commercial products, offering anywhere between a single slot or 8 slots.

  • Heck, there are even PCIe to ISA bridges except they are usually a bit expensive.


*1 - Legally, going by the FCC ID BOU, by Philips Consumer Lifestyle of Hong Kong.

*2 - Not to be confused with the 1901 colour monitor, based on a Thomson model, that got sold with C128 and early PC10 (for CGA Mode).

*3 - While 75BM13 sounds like directly taken form Philip's name for the green version BM7513, Commodore used it (only) for the amber one.

*4 - You may want to take a look at the German Wiki entry for the PC10, containing a bit more information, as these machines were not only developed at Commodore Braunschweig, but also quite popular as 'high quality' clones.

*5 - Advanced Graphics Architecture - not to be confused with the later Amiga Chipset of the same name - which got in turn named AA in Germany :))

  • Do you have links to USB-to-ISA boards? I only know of the ARS Technologies boards, which are expensive and limited (no IRQs or DMA), and effectively only work with their special build of DOSBox which redirects ISA accesses to their USB device. – Stephen Kitt Nov 1 at 13:46
  • @StephenKitt Ups... good question. I have seen some home build on vintage meets over the last years. then again, but did not pay much attention. Personally I have used a PCI to ISA bridge card around 2000 - no loner with mer, but much like this one: costronic.com.tw (klick onPCI ISA and then CV71). And for PCIe there's the iWave chipset which I never have used. Drivers are always a problem, as ISA access was an hardware issue in itself, not as easy to handle for modern boards. Solibraries are a must. – Raffzahn Nov 1 at 14:38
  • @StephenKitt Thinking of it, I get an urge to build a USB-to-ISA adapter myself. Let's see if I can withstand :)) – Raffzahn Nov 1 at 14:39
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The monitor shown is a Philips BM7523 which is a 12 inch amber monochrome MDA/Hercules display. The cable shown in your photo ends in a DE-9 plug which is standard for MDA, CGA, and EGA. (VGA uses a DE-15/HD-15 connector.) The service manual with specifications is here.

First, you might be able to put your VGA adapter into a mode whose timings are compatible with MDA without releasing any magic smoke. If not, read on...

MDA has a resolution of 720×350 while VGA is 640×480 or 800×600, so the first problem is to figure out how to squeeze or stretch a VGA resolution into an MDA resolution, and how to handle MDA's non-square pixels.

Edit: Raffzahn's answer says your particular monitor supports 800 pixels across, so that helps a little.

The next problem is that MDA is monochrome and supports only 3 levels of brightness per pixel (off, low intensity, high intensity).

Once you've decided how to deal with the mismatched resolution and colors, the technical hurdles begin, starting with converting VGA's horizontal 31.469 kHz and vertical 59.94 Hz scanning frequencies to MDA's horizontal 18.432 kHz and vertical 50 Hz frequencies. You will need to constantly capture the VGA signal to a RAM frame buffer 60 times (frames) per second, and read the same RAM to create an MDA signal 50 frames per second while doing the conversions you decided upon above.

But now you have one more conversion: converting 60 fps progressive to 50 fps interlaced. You'll get some judder or tearing depending on how you do it. If you're adapting from HDMI, you could avoid the problem by sending the monitor a 50 Hz PAL signal.

All of these problems can be overcome, but not without tradeoffs. You might design your VGA/HDMI to MDA adapter in an FPGA due to tight timing requirements and lack of modern supporting chips.

One more thing, this monitor has a long-persistence phosphor, another reason why it won't be very good for video or games. If I were you, I would keep the monitor in its native habitat by finding a nice old computer that outputs MDA/Hercules. Then if you still want to connect this monitor to a modern computer, you can do that through RS-232 and a terminal emulator running on the old computer, with perhaps getty running on the modern computer.

  • 1
    "The next problem is that MDA is monochrome and supports only 3 levels of brightness per pixel (off, low intensity, high intensity)." The screen is not specific to the 4 levels MDA provides, but takes intensity as analogue value. So it may very well work with a combined RGB value (resistor network) – Raffzahn Nov 4 at 21:03

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