How to synchronize presentation on the front panel to the start of a 75Hz monitor's retrace cycle?

How to synchronize front panel presentation with the start of a retrace cycle of a 75Hz Monitor, so when a bitmap is presented 100ms, its duration is indeed 100ms on the monitor?

Hi,
In the old days (late 90's), we used in port and out port to wait for
vertical retraces (or even horizontal retraces).
I searched the web (vertical retrace), and there seem to be lots of
infromation and tools, like
http://www.compuphase.com/vretrace.htm
It uses a simple routine:
mov dx, 3dah ; VGA input status register
vretrace_loop:
in al, dx
test al, 8 ; bit 3 set?
jz vretrace_loop ; no, continue waiting
But to get it working, you need a VxD. Good news is you can download it.
The also suggest you use WaitForVerticalBlank(), but dx could be hard to get
working under LabVIEW.
Please let us know how (and if) you got it working with LabVIEW!
Regards,
Wiebe.
"Vinci HK" wrote in message
news:[email protected]...
> Hi Robert,
> I am so excited to have received a response! Sorry that I didn't reply
> earlier as I have been out of town. You are understanding the problem,
> so good!
>
> I just want to know the exact duration a stimuli in the front panel is
> presented. I can make it to last for 13 frames, but the problem is to
> ask LabView to synchronize with the start of a frame.
>
> The crucial thing is that I want a trial of presenting 700ms blank
> screen + 1300ms bitmap will add up to 2000ms on the front panel. And
> in the next 2000ms, a different bitmap will be used for the 1300ms.
> The start of a trial is initiated by a pulse from the parallel port. I
> need the 2000ms on the front panel to be really 2000ms+/-5ms.
>
> My worry is that even if I buy the external clock and the RealTime
> system of LabView, I won't be able to get the front panel to
> synchronise with the refresh cycle of the monitor, so that the trial
> length as it appears on the front panel is 2000ms +/- 5ms.
>
> What do u think?
>
> I am using LabView for my fMRI experiment, and I wonder if you know
> anyone from the fMRI community who are using LabView for stimulus
> presentation and synchronization with MRI data acquisition?
>
> Thanks,
> Vinci

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"Gert" wrote in message
news:8uto76$r8v$[email protected]..
> I have deleted the Attribute Node setting a control in a cluster to
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>
>
> Sent via Deja.com http://www.deja.com/
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How to synchronize presentation on the front panel to the start of a 75Hz monitor's retrace cycle?

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