The Atari ST/STF/STE supports 3 resolutions:

  • Low (320x200),
  • Medium (640x200) and
  • High (640x400).

As far as VGA is concerned, this can be divided in 2 groups:

  • The “Low” and “Med” resolutions output an RVB signal that would be compatible with VGA except that it has a horizontal sync rate of 15.625 kHz which is too slow for most VGA monitors can display (it’s more a “TV” sync speed; very very few VGA monitors can display it).
  • The “High” resolution outputs a monochrome signal (but we can easily “triple” it and feed the same signal to R, G an B) and, good news: it has a horizontal sync frequency of 35.8 kHz which is compatible with the specs of virtually all VGA computer monitors.

So, while the Atari ST never came with a VGA cable, it’s actually possible to build one, at least for the High resolution mode. Here’s a step by step guide to make one:

My cable is a simplified version of this schematic:

In my case, I’m not using any resistors (see at the end that it still works).

Start by cutting an old VGA cable in half. We’re going to use one half as is an attach a DIN-13 plug (which is still easy to buy on the Internet).

Before doing anything else, don’t do the same mistake I make every time: do not forget to put the DIN-13 sleeve onto the cable! You can’t put it there later:

Next, remove the isolation and use an ohm-meter to identify all the wires we need:

Colors may vary for your cable, so make sure you use the pinout and an ohmmeter to identify them correctly.

Next, join the Red, Green and Blue and prepare a thermo-shrink tube:

These 3 sould be soldered to Pin 11 on the DIN-13 (the “Monochrome out” will send the same signal to R, V and B):

If you can make a nicer solder joint than I did, good for you ;) No matter what, protect with heat-shrink tube as the DIN-13 pins are very close to each other:

Then solder the H-Sync to pin 9. Again prepare Heat Shrink Tube:

And shrink the tube:

Here you can see my tube is all dirty because I though it was a good idea to shrink it with the tip of my soldering iron. Don’t do it like me. Use hot air instead. (A girl’s hair dryper does the job, if needed ;)

Next comes V-Sync on pin 12. Agin, don’t forget heatshrink tube:

Then we’ll need to connect pins 4 and 13 to GND. In my case I’m going to connect those pins to the Shielding and other GND wire (the black one) in the back side of the connector, because the pins are already crowded. So I’m just soldering two short wires here. Note that for the main GND on pin 13, I used a thicker wire to be on the safe side:

The isolation of my pin 13 GND wire had melted a bit but it’s still okay…

Next, all the GNDs must be connected together, and also connected with the shieldings:

Does it work?

Yes it does:

There is some moire on the photo, but in reality the image quality is pretty good:

For reference the display I am using here is a SONY SDM-S95R it has DVI-D and VGA inputs. It also has audio passthrough to a 3.5mm jack on the side but no internal speakers.

Does it always work?

Not really…

First I tried on a Samsung TV which has a VGA input:

Auto adjust fails completely. But even after 15 minutes of tweaking all the settings, I never could get a better picture than this:

  • Contrary to the SONY, the grey background pattern is impossible to get clear from left to right (the pitch setting range is not wide enough).
  • It’s also impossible to get the picture correctly centered and/or sized and there is a part missing on the right that is impossible to display.

I’m not surprised that the Samsung TV is worse than the SONY monitor but still… this is really bad :(

Next, I tried to pipe the VGA through converters to display it on an HDMI monitor. Here I either got nothing on screen, or this:

TODO Next:

  • Try other VGA to HDMI adapters (Amazon has plenty)…
  • If none works, maybe I should use resistors in my cable after all? (unlikely cause)