Amiga-VGA Cable

This is the project for people who want to use either a multisync or a PC VGA monitor on their Amiga but find that all the sync signals are wrong. Note that in the case of the VGA monitor, it will not let you use lower frequency screenmodes. That is the job of flickerfixers, which are more expensive and a billion times more complicated.

All that really needs doing it making the connections for the RGB signals, the sync signals and a couple of ground signals. However, this sounds all to easy and it is. The sync signals need inverting, that is when the Amiga puts a high (1) on the sync line, the monitor is expecting a low (0). For this reason all you will get without the inverted signal is trash.

The easiest way to invert the signal is to use a Hex Inverter, or a NOT gate as it's often called. This does exactly what it says, and inverts the signal, 1 to 0 and vice-versa. However, another way and one that is just as easy is to use a NAND Gate, with both inputs hardwired together. This is often easier to follow on instructions as the inputs are more standardised than NOT gates, so my diagram uses these. By putting the sync signal through one of these apiece, you can change it to be what the monitor expects. This is a very small bit of hardware physically, it is perfectly possible to get it inside the 23-pin connector shroud at the Amiga end.

One last item you may need is a bit of buffering. Although sometimes you won't need it, it doesn't hurt to put it in and for the minscule amount it costs it's worth it. What happens is the Amiga uses it's H and V sync lines for inputs. This happens when you are using a genlock which doesn't need sync signals. So when the Amiga thinks it has a genlock on the video port, it won't provide those sync signals. The easiest way to avoid this is to use a capaciator (100µf) to provide buffering, just insert it between GND and +5v. This is enough to take away that risk.

Now lets have a look at that in graphical form:

Textually it goes something like this: 


     Amiga 23-pin      PC 15-Pin HD     7408 NAND       Signal
     ------------      ------------     ---------       ------

          1                 1                           Digital Red
          2                 2                           Digital Green
          3                 3                           Digital Blue
         11                                1,2          V. Sync
         12                                4,5          H. Sync
                           14               3           /V. Sync
                           13               6           /H. Sync
         19            4,5,7,8,9,11         7           Ground
         23                                14           +5v

Parts you will need:

You will also need a good quality soldering iron and some fine solder. A multimeter would come in handy too.

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