Classic Computer Magazine Archive COMPUTE! ISSUE 77 / OCTOBER 1986 / PAGE 10

Standard RGB Monitor With ST?

Is there any way to hook up the Atari ST to a standard RGB monitor? If not, do you know of any products on the way from third-party vendors that will facilitate this? My Magnavox CM8562 monitor has an eight-pin DIN socket.

Don Kusch

To address your second question first, no such product is commercially available at the time of this writing (July, 1986). There are two major difficulties standing in the way of such an interface. The first problem has to do with hardware availability. The ST end of the video connector requires a nonstandard 13-pin plug which is next to impossible to find—even if you're a commercial cable manufacturer.

Second, in addition to sending out video signals, the ST's video port makes it possible for the computer to tell whether you're using a monochrome or color monitor. Pin 4 of the connector is the monochrome-detect line. When the voltage level on pin 4 is low, the computer automatically boots up in high-resolution monochrome mode. When pin 4 is set high, the computer boots up in color mode. The ST monitors pin 4 continuously. Whenever it detects a a voltage transition on pin 4 (for instance, if you unplug the video cable), the computer performs a cold start.

Assuming you can find or fabricate a usable 13-pin connector, you must also find some way to hold pin 4's voltage at the correct level. The video port doesn't provide a voltage source appropriate for this purpose, so you must obtain it elsewhere. Perhaps the safest source would be a commercial power supply. An experienced electronics technician might be able to tap a suitable source somewhere in your monitor's circuitry, but that sort of experimentation is best left to professionals. The power supply in a TV or monitor carries potentially fatal high-voltage current. Once you surmount the monochrome-detect problem, you may have other problems matching the ST's audio and video signals to the requirements of your particular monitor.

We've heard from one brave soul who succeeded in cobbling together a homebrew ST interface for his Sony KV-1311CR monitor. He obtained a 13-pin plug by the simple (but costly) expedient of buying a replacement video cable from Atari and chopping it in half. By the time he finished the project—which involved tapping into the Sony's internal circuitry—his investment ran close to $100, including the cost of the Atari cable. We've never seen the finished product, so the picture and sound quality on that system is unknown. Since it involves modifying the monitor itself, only a technician could tell you whether a similar solution is practical on your Magnavox monitor.

In short, it's possible to construct such an interface, but at this stage it's strictly a do-it-yourself project for the sophisticated hobbyist. As the ST becomes more popular, it seems inevitable that some enterprising manufacturer will market a video interface for non-Atari RGB monitors. If and when that product appears, it will probably cost more than a conventional cable, due to the need for extra circuitry.