Hi Gordyh, just so I make sure I understand correctly, your set up is as follows:
PXI 6366
- Analog Output Waveform
- Start Digital Edge: Source PFI0
- TTL Sync Connected to PFI0
External Signal Generator:
- Analog Output
In order to have synchronized output, you need to share the output signal generator's clock as well as the trigger. You currently have a shared trigger, so they will start at the same time, but the sample clocks are not synchronized, so I'm not surprised you're seeing drift. I'm not sure if this external signal generator you're using can export or import a sample clock, but I do know that the PXI system can PLL clocks through the backplane and have synchronized reference/sample clocks.