🚀 go-pugleaf

On Mon, 05 Mar 2007 19:47:16 +1100, in sci.electronics.design Lionel
<usenet@imagenoir.com> wrote:

>Per the subject line. I want to experiment with direct PAL video
>generation from a microcontroller, with the minimal number of parts.
>I'm thinking that a good starting place might be to use a CPU clock
>that's based on the PAL subcarrier frequency (4.43MHz) multiplied with
>a PLL+VCO+Divider to give me phase reference points, & directly
>generate the composite colour signal via an R2R ladder.
>
>So, some questions:
>
>1) Is this a reasonable concept? (I'm comfortable with per-cycle level
>timing & coding)
>
>2) Any tips/suggestions/thoughts as to a better approach?
>
>3) What's a good (simple, cheap, stable) circuit to oscillate a
>standard 4.43MHz PAL sub-carrier xtal? (Ideally just an inverter or
>two)
>
>4) Suggestions for a cheap + simple PLL frequency multiplier (x8? x4?)
>for the above to give me multiple cycles per PAL subcarrier cycle?
>
>5) How many analog samples do you actually /need/ to generate per
>subcarrier cycle to get good quality PAL colour?
>
>6) Any recommended online resources/references that cover direct
>digital synthesis of medium to high quality PAL colour video?
>
>Thanks in advance for any help or advice.

Normally PAL/NTSC is samples at 4 times subcarrier. There are some
genlock ics around see here:
http://www.intersil.com/products/pt/parametric_table_10395.asp
You may have to find out all the joys of the "eight field sequence",
fortunately, I have forgotten most of it, it's messy.

Maybe you should think about working in YUV/component/RGB, which has
no subcarrier, but is  sampled at 27M/sec, and is easier than PAL

List of chips: http://www.epanorama.net/links/videochips.html


martin