Indivision AGA MK3/hacking
Indivision AGA MK3 comes with an adapter that plugs over the CIA chip of the A1200, A4000T or A4000D. In case that CIA chip is not accessible, you can find a few hints here about where to access these signals in other places. Please note that this information comes without warranty, and we highly recommend assistance of a professional if you have not done any SMD soldering yourself yet. We do not accept any responsibility for possible damages that result from using this information or from unsuccessful attempts of accessing the signals in other places. The only recommended method of accessing these signals is by using the included CIA adapter. If you choose not to use it, you're on your own.
pinout of the Indivision AGA MK3 components
Indivision AGA MK3 uses four additional signals: KBClock, KBData, Fire0 (=left mouse button) and the power LED signal. The pinout at the flicker fixer can be seen in the left picture - the orientation is exactly as if you're looking down at the installed flicker fixer in an A1200.
For completeness, the pinout of the CIA adapter is also shown. Again, the orientation is the same as if you're looking down on the installed unit in an A1200.
other locations of the signals
locations on the top side of the A1200 motherboard
The keyboard signals are especially hard to access from the top side of the A1200. If you feel confident enough, you can access them at the keyboard controller chip. The LED and left mouse button signals are fairly easy to access, as soldering a wire to a terminal of a resistor is rather easy (well, compared to soldering to an SMD chip).
Unfortunately, the Power LED signal is not easily accessible on the bottom side of the A1200 motherboard. However, the keyboard signals are rather easy to access, and there's a hole in the board that can be used to route the signals to the top side of the board. This hole is meant for the harddrive cradle, which is not used in most cases anyway, as it may make a short with the flicker fixer, and real harddrives are often replaced by CF cards for lower noise, lower power consumption and higher capacity.
pinout of the 22-pin connector
This connector looks very much like a clock port, but it's certainly not. Likewise, the long cable that's included with Indivision AGA MK3 should NEVER be used on a clock port of an A1200, as the bus signals are unbuffered and not meant to be routed through a cable that's longer then 120mm. The output of Indivision AGA MK3 has proper cable drivers, and given proper cable termination, you can expect good picture quality up to 5 meters of total cable length. The pinout is carefully chosen to resemble coax-cables and to take advantage of the parallel routing of the flat cable: Analogue signals have ground guard-traces, and the digital differential signal pairs are routed in parallel. Note that the 5V_DDC should not be loaded too high, and that in reality, it will only carry around 4.8V, as the flicker fixer has a protection diode to prevent reverse current flowing from the monitor into the computer.