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PICList Thread
'The caption multiplexer'
1997\07\09@120548 by David Moisan

picon face
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).
>
>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.

Dave
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1997\07\10@034412 by John Payson

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face
> 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"!)

1997\07\10@104515 by Engineering Department

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face
----------
> Via: John Payson
> > 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.

The bummer is that Philips and Motorola are dropping the CC chips they
have.  Zilog is changing to a new design -- but, after bugging them daily
for information over the past two weeks they still don't have anything but
a data sheet.

Philips just announced a new monster (40 pin PLCC, I think) CC chip.
Again, it seems to be just a press release at the moment.  I haven't gotten
a data sheet yet.

Could be that like the earlier Motorola and Zilog chips this current crop
is designed by EEG -- Motorola or Zilog are just the foundry reselling on a
royalty scheme.  The problem is that EEG technical support is second only
to Microsoft <g>, so I wonder if these new chips (like the previous
versions) stand a chance of ever being adopted.

The Zilog data sheet is pretty good, but there are the inevitable gaps in
things like the way they impliment their communications on the SPI (it has
an I2C for PICs) bus.

Cheers,

Win Wiencke
Image Logic Corporation
ImageLogicspamKILLspamibm.net

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