> At 12:01 AM 7/9/97 -0400, you wrote:
> >> Hi John,
> >>
> >> So what was (is) the caption multiplexor?  I'm curious.
> >
> >It was a piece of hardware/software which would add information to the
> >"Caption Channel 2" which is available on any TV that supports captioning,
> >and would also add information to "Text Channels 1 and 2" which are avail-
> >able on 90% of CC TV's.
> >
> How did you handle the encoding?  You don't see too many single-chip
> caption encoders out there (excepting the DTV chips used in digital
> satellite service).

Well, I intended the design for both closed-captioning and OSD
applications (though I could never get a PLL to work well enough for OSD
to be worthwhile).  The digital part of the design used an 87C51, two
PLD's, a 32Kx8 SRAM, and a 1Kx1 SRAM (used to capture the incoming
captions).  One of the PLD's handled dot-clocking while the other served
as a column-address counter; the CPU output row addresses directly.  The
analog part consisted of a few Maxim and Elantec chips.

In some ways, the design was pretty clever.  In other ways, in retrospect,
it was not so good.  Nowadays, I think the best approach would be to
simply use a PIC running at 10 or 20Mhz  or thereabouts and have it do the
captioning with minimal extra junk.

> >Neat capability.  Too bad it didn't go anywhere.
> Side note:  Some CC chips I've seen do the OSD (on screen display)
> functions as well, the Philips SAA5252 and the Zilog Z86129 the chips I
> know of.
> The Zilog chip seems really nice, doing extended data service (V chip!) as
> well.

True, though I prefer television sets (such as my own) where the OSD is
handled seperately from the captioning.  It's rather irksome otherwise to
have the on-screen messages override the captions (esp. "MUTE"!)