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Date Posted: 06:14:18 01/31/02 Thu
Author: Potter
Subject: Re: Need expert help please!!!!!
In reply to: Tom 's message, "Re: Need expert help please!!!!!" on 21:34:27 01/30/02 Wed

All the 3chip code versions I've seen rely on the signature pulses at the end of the Vsync period to lock onto the signal (line 6 for NTSC and line 3 for PAL).
The signature is:
minimum 18uSecs of quiet (no PEDs or NEDs)
then PED
NED 4.6uSecs after PED
PED 2.6uSecs after NED
LOCKON then checks to ensure several following edges occur within specific time windows to identify odd/even frames and eliminate false locking.
MAKEVBI checks for edges generated by the actual serration pulses each frame to determine if lock is still good.
MAKEHLINE actively maintains lock by speeding up/slowing down the oscillator according to the position of the actual Hsync pulses.
It could be that the company has found a way to screw up this technique - the arms race continues.....


>The only way I can see to do it with the information
>available is to use a momentary switch and do it
>manualy. The switch would tell the PIC to skip lines
>until the VBI bar is hidden and when the switch is
>released, the picture should stay stable until it
>loses lock. This would require removal of the check
>lock code in the MakeVBI and modification of code in
>the Main routine for skipping lines.
>
>If there is any identifying characteristics that are
>repeating in the VBI, then that can be used to locate
>the VBI. The code could also be written more like the
>Maxi* code where it looks for a hsync pulse and if it
>doesn't see one, it assumes that the VBI is starting.

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