It turns out that an IBM CGA monitor will work if you invert the
horizontal and vertical sync signals. I did this with a simple
7400-series TTL inverter chip. I put it in a small box which gets
connected as shown below:
+-------+ +----------+ +---------+
| | | | | |
| S-550 |--------->| inverter |--------->| CGA |
| | | box | | monitor |
+-------+ +----------+ +---------+
Power for the inverter comes from one of the pins on the S-550
digital video output.
From memory, I believe the pinout diagrams for the video output
in the S-550 manual are correct; I think they show the 8-pin DIN
socket on the sample with positive sync signals. The pinout shown
for the type of connector on the CGA monitor has negative sync
signals, so I tried the inversion.
People have told me that some Atari monitor works without an inverter,
so I would imagine that some monitors accept non-inverted sync signals
(or perhaps they can use either polarity). The Apple monitor may be
that type.
Anyway, this worked for me.
(
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