Hmmm. I'm not sure what XDS is, but I've designed two surveillance camera
controllers and 3 robots using a form of interlace code (VITC-like), all
using PIC, on NTSC lines 12 and 13.

The problem with a 20/40mhz PIC is that it can't keep up with a single
pixel, so can't directly generate or read the visual text codes (for deaf
persons). BUT, it can send/rcv a reliable control signal capable of
controlling cameras or robots that is 16bits wide. The way my stuff worked
was that the operator would grab the interlace lines with a PIC and send
control packets (white on black)on top of the actual video signal coming
FROM the camera or robot! The PIC receiver in the robot would extract the
control packet (17 bits + 2b CRC) and control the camera or robot position.
Worked reliably to about 200m of cable. The command was only honored if the
CRC was correct.

To extract text codes, a hardware chip (or CPLD) is needed to count pixels,
extract information, and jam a FIFO. The FIFO is then read by a PIC or
whatever.

I wasn't aware that time codes were sent on the interlace; I know that
commercial news broadcasts publish "frame counts" on a recording as a
routine measure so that splicing can be done seamlessly.

Am I not understanding what you are asking?

--Bob


At 02:21 AM 11/26/2003, you wrote:
>(If this is the fourth copy of this I apologize up front. Webmail
>interface is screwy tonight.)
>
>
>We feed our boob tube Directv so getting the PBS time signal to the VCR
>requires some thought.
>
>I could stick up an antenna to catch the local stations and feed that to
>the VCR but that wouldn't require a PIC.
>
>http://www.robson.org/gary/writing/nv-line21.html#
>
>I was thinking of feeding a GPS or NTP time signal to a PIC and have it
>generate VBI line 21 data.
>
>Anyone looked at decoding or generating XDS packets with a PIC?
>
>--
>http://www.piclist.com#nomail Going offline? Don't AutoReply us!
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--------------
Bob Axtell
PIC Hardware & Firmware Dev
Tucson, AZ
1-520-219-2363
"I lose some on each sale but make it up in volume."

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