Sorry, I was writing my post while you made your post. Taking the signal off the board is an option, but then the two boards are physically locked together. I really don't want to do this if I can avoid it. The video processing on the Prop will be in software. I'll read read the H Sync, V Sync and video signal with three of the Prop's I/O pins. The actually processing will be going on inside the Prop. Essentially what I'll be doing is turning the Prop into an oscilloscope. The software will be reading the video input pins at a higher frequency than the Mac provides and acting appropriately when the video signals change from low to high or high to low. Basically, the video will be interpreted. A bitmap will be generated from the video signal and displayed with some simple VGA circuitry.

You are correct about the hub RAM, but that is a minor issue. It is trivial to add extra external RAM if needed. Also, the Prop has a 32K code limit and the code is stored on an external EEPROM. It is very common to use 64K or larger EEPROM's for the purpose of adding extra memory.

I was unaware that the PLL only works with frequencies under 8MHz. Thanks for the tip. This is trivial. I'll just use a shift register to divide the clock down to 7.8336 MHz to drive the Prop and use the 8x PLL.