68kMLA Classic Interface

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Looking for help from owners of IIvi, IIvx, LC I, LC II, or older NuBus video cards with a scope or logic analyzer
Posted by: bigmessowires on 2023-10-16 15:08:44
I'm working on a mostly useless Mac-to-VGA adapter prototype with integrated sync splitter, and I could use some testing help. If you have one of these Macs or video cards:
  • IIvi
  • IIvx
  • LC I
  • LC II
  • Q900
  • Macintosh High-Resolution Video Display Card (630-4222 / 630-4230)
  • Macintosh Display Card 4-8 or 8-24
Please try this: stick a piece of wire in your DB-15 monitor port to connect pins 4 and 6 - this makes the Mac think a 13" RGB monitor is connected. Then connect an oscilloscope or logic analyzer (ideally with analog capture capability) to each of pins 3 (CSYNC), 15 (HSYNC), and 12 VSYNC. What do the signals look like? Post some screen captures from your scope if you can. Especially try to examine what the signals do every 1/67th of a second during the vblank interval.

I am interested in getting direct proof of which systems output CSYNC only, and exactly how the CSYNC signal looks, and which systems also output separate HSYNC and VSYNC signals. These particular Mac models and cards are in the gray zone where I'm not sure what to expect. Anything newer than these will output separate HSYNC and VSYNC signals.
Posted by: Phipli on 2023-10-16 15:12:05
Please try this: stick a piece of wire in your DB-15 monitor port to connect pins 4 and 6 - this makes the Mac think a 13" RGB monitor is connected.
One of these might be a nicer way of doing it.

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I have an LC and possibly both of the Nubus cards.
Posted by: bigmessowires on 2023-10-16 16:00:52
For sure if you have a DB15 breakout, it's a bit more convenient, but sticking wires into the holes also works. 😛
Posted by: Phipli on 2023-10-16 16:23:15
For sure if you have a DB15 breakout, it's a bit more convenient, but sticking wires into the holes also works. 😛
Surely we all have a pile of those, with different pin counts and genders, in a box? They even do HDMI ones 😛

How else do you plan to connect your home brewery system to your Centris 650's National Instruments NB-MIO-16X?

🤣
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