Have you considered using one of the OSD (On Screen Display) chips ?

Look for example for 'OSD' in
http://www.semiconductors.philips.com/catalog/219/282/31111/31542/index.html
#31542

Other companies have similar offerings.

Tal

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Olin Lathrop
> Sent: Sunday, June 02, 2002 6:58 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]:Having problem with pic clock
>
>
> > I am using PIC microcontroller (4 MHz crystal) and LM1881 to add a white
> > box to
> > composite video at a specific location on TV. The problem i am having
> > is that the box is not stable and moves on TV horizontally.
>
> That means you have some jitter in your response time for
> starting the white
> box signal.  With a 4MHz PIC the response will have 1uS jitter at best
> unless the clock is somehow synced to the vide.  The jitter could be much
> more depending on how you are trapping the signal and getting the
> PIC to do
> whatever it is supposed to do.  I don't think a PIC (or most any
> microcontroller) is a good choice for generating video that is externally
> synced without some special sync circuitry.  It would be a lot
> easier if the
> micro could generate the sync itself.
>
>
> *****************************************************************
> Embed Inc, embedded system specialists in Littleton Massachusetts
> (978) 742-9014, http://www.embedinc.com
>
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