[this thread split from David Prentice's original thread about TFT-SPI displays]
I may have mentioned this before, but I haven't yet found a cheap TFT module that brings the VSync line out to the connector. This is a bit of a pain if you want to have tear-free screen re-writes. In fact even a register bit that could be polled would probably be good enough.
John, I did a lot of searching and investigating.
All the 37 pin modules you find on ebay have pin 21 marked as N/C.
Pin 21 seems to be a general purpose pin that gets used for different purposes in OEM applications.
Because sometimes it is an input and sometimes an output when they get sold after-market they leave this pin open.
I found that the 2.8" ILI9325 sold by the ebay seller "coldtears" has a 0402 sized resistor unpopulated on the FPCB.
When I traced the copper leading to the IC DIE and matched up the other pins with the data sheet it looked like it lead to FMark (the frame flyback output).
Long story short. Populated R6, programmer the ILI9325 to output FMark and I was in luck.
There may be a lot more of them on ebay that have the FMark output. I only bought tried two and the one from "coldtears" was a success. The other looked like it went to IFx to set the unit in 6800 mode.
With FMark I have a pretty flash little AVR games system.
With some fancy AVR tricks I can clear pixels at 8M Pixels/S and draw lines/sprites at between 0.2 and 1M pixel/S. All synced to the frame flyback for flicker free awesome.