HSYNC / VSYNC waveform fussy on a 1409?

[K1200LT_rider]

We have a custom line camera signal that we are having partial success in capturing.  It is externally triggered with an external 12 MHz PCLK being fed in.  After rebooting a cold computer (it's been off for a while) we open the MAX IMAQ capture screen for channel 1 under img0.  For about 1/2 a minute or so we get continuous captures using Grab.  It's horizontally sync'ed, but not vertically (it slowly rolls upward).  The pixels are being captured pretty well.  Then the capture freezes in the utility and I get the pop-up window that says something about not seeing a valid video signal.  Using an o'scope, we see that our video signals are still there and look unchanged.  We are using TTL signals for HSYNC, VSYNC and PCLK.  Due to some circuitry we had to insert as an interface, the HI amplitude of the TTL sync signals is about 3 to 3.2 V, which is well above the TTL minimum of 2 V for a HI, so I'm assuming that's OK.  I'm very puzzled as to why we don't see the vertical sync'ing at all.  Using an emulated video signal that I coded and generated by a NI 5411 arbitrary waveform generator, the 1409 was capturing beautifully using the same-looking VSYNC signal - other than the fact that the AWG was putting out 4 V for a TTL HI for all the digital signals.  However, the HSYNC from our real unit does not quite match what I was generating in the AWG.  According to the preliminary spec we got from the developers, I programmed the AWG to put out perfectly consistent, narrow, HI HSYNC pulses throughout the entire frame.  But the HSYNC from the real unit is inverted during the time period between the frames (normally HI with narrow, LO pulses).  I'm thinking that this may be messing up the PLL inside the card so it can't maintain horizontal sync.  But why would it work for a half minute or so before it quits working?  We've shut down the computer and tried rebooting several times, but it never will start capturing again unless we completely turn off the computer and let it cool down (with the PCI-1409 card inside).  Then on a reboot it works for the half minute.  We've tried other channels on the card and they don't work any better.  I know all the channels on the card have worked with the emulated video signal from the AWG.

In general, is there a minimum or maximum pulse width for HSYNC and VSYNC for reliable 1409 operation?

If we can't get this card to work reliably with our video signal we'll have to go to a digitizer. 

[jpaul]

Hi K1200LT,

Thank you for your detailed problem description. As a result of looking through it, I have a follow up question:

- It is exactly the same amount of time before you the invalid video signal error every time that you have run the test?

If so this may point to a skewing issue with your video signal itself. Please let me know and in the mean time I will research further into potential causes of the issue you are seeing.

Regards, 

[jpaul]

K1200LT,

Another suggestion based on your response is to try to mimic the HSYNC from the camera on your AWG (your AWG voltage levels should be sufficient). Look forward to your response.

Cheers,