When the ST was designed, there were two contrary ideas, how this machine should be used. On one hand, there was the Apple Macintosh, with its clear and sharp but monochrome displays. On the other hand, there was the more casual use, like games and graphics, that Atari knew the upcoming Amiga would offer.
So the idea was to basically have two different video modes: One with a high resolution but no colors for "serious" business use, and another with less resolution and more colors. When the first machine was introduced in 1985, it came out with three display modes:
- 640 x 400 pixels, monochrome
- 640 × 200 pixels, 4 colours
- 320 × 200 pixels, 16 colours
It's a female 13-pin DIN connector with the following pinout:
- Audio out
- not used on ST, on STE: Composite Video (if RF-modulator is present), Composite Sync (no modulator)
- General Purpose Output (External Clock select on STE)
- Monochrome Detect (External Clock in, when on STE and 3. is grounded)
- Audio In
- GND on ST, 12V on STE
- Horizontal Sync
- Monochrome Video
- Vertical Sync
Since these are regular TV standards, you could connect the ST to a TV that provides analog RGB inputs, for example via a SCART cable like this one: http://info-coach.fr/atari/hardware/int ... itel_cable. At least this was the intention at that time. The Atari SC1224 was another option, it used a cheap and small TV CRT and was often sold in bundle with the computer.
The high resolution with its 640 x 400 pixels went beyond TV specs and needed a special display at that time, which Atari provided in form of the SM124. In order to not damage the connected display with a wrong signal, there is a pin on the connector, that tells the system at bootup, what display is connected. If pin 4 is grounded, high res is used, otherwise it defaults to low res. It would not need RGB signals, only a single monochrome video signal. But it needed a higher horizontal sync frequency of 35.7 kHz and 71.2Hz vertically. The resulting image quality made this a very popular combo which was sold as a bundle as well.
This lead to the situation, that if you wanted to use all resolutions on your ST, you would need two displays, and had to unplug and plug, if you switched. NEC was the first (I believe) to introduce a so called Multisync-Monitor, which was capable of not only having a fixed frequency, but syncing to a bandwidth of input frequencies, hence the name. With a monitor like this, you could use all three resolutions, provided you had a cable, that allowed the switching of high res.
Conveniently exxos has a adapter in his store, that solves the latter:
So if you find a old Multisync-capable monitor, that supports 15.75-35.7 kHz vertical frequency, you are ready to go.
In order to operate your ST on a more modern display, you will have to solve the following issues:
- The ST outputs analog signals, modern displays (TVs and Monitors) often require digital signals
- Switching between high res and low/med res if not using two displays
- the display handling 15.75-35.7 kHz horizontal sync frequency, since most displays only start at 31kHz, which would be a VGA signal.
There are still Multisync-capable TFTs out there and there are some lists floating around, that try to give recommendations. We try to compile a list of our own, depending on the informations we find. This TFTs could be used with the adapter mentioned above as well.
The last option is Scaler/Signal converter that provides the analog inputs, internally digitizes and upscales them in order to output them digitally to a modern TV/TFT with HDMI inputs. There are different choices out there, and we will post some experiences here as well.