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From: Jacek Mazurkiewicz on 6 Feb 2005 02:22
Can anyone give me an idea as to the bare minimum system requirements for
generating the picture information for some NTSC video at a very low
resolution?

I'll be working with a small 8085 microcontroller for which I don't yet have
the exact specifications (it either operates at a 1KHz or 1MHz clock
speed), and I was wondering if I could somehow use this to generate a
composite video signal, or if the microprocessor is underpowered for such a
task. I'd need some auxillary circuitry to generate the video sync
(possibly using an LM1881). If anyone here who's done something similar
wouldn't mind giving a few pointers to a newcomer, please post any
information that you think might be useful to know.

Thanks
Jacek Mazurkiewicz
From: CBFalconer on 6 Feb 2005 06:11
Jacek Mazurkiewicz wrote:
>
> Can anyone give me an idea as to the bare minimum system
> requirements for generating the picture information for some NTSC
> video at a very low resolution?
>
> I'll be working with a small 8085 microcontroller for which I
> don't yet have the exact specifications (it either operates at a
> 1KHz or 1MHz clock speed), and I was wondering if I could somehow
> use this to generate a composite video signal, or if the
> microprocessor is underpowered for such a task. I'd need some
> auxillary circuitry to generate the video sync (possibly using an
> LM1881). If anyone here who's done something similar wouldn't
> mind giving a few pointers to a newcomer, please post any
> information that you think might be useful to know.

It's an 8080 with a few added instructions, and usually operates at
2 to 8 Mhz. Minimum 4 clocks per instruction. Last seen in the
first Mars lander.

--
"If you want to post a followup via groups.google.com, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson


From: Peter on 6 Feb 2005 06:19

"Jacek Mazurkiewicz" <jack(a)jessmaz.com> wrote in message
news:gBjNd.3179$wK.468(a)newsread3.news.atl.earthlink.net...
> Can anyone give me an idea as to the bare minimum system requirements for
> generating the picture information for some NTSC video at a very low
> resolution?
>
> I'll be working with a small 8085 microcontroller for which I don't yet
> have
> the exact specifications (it either operates at a 1KHz or 1MHz clock
> speed), and I was wondering if I could somehow use this to generate a
> composite video signal, or if the microprocessor is underpowered for such
> a
> task. I'd need some auxillary circuitry to generate the video sync
> (possibly using an LM1881). If anyone here who's done something similar
> wouldn't mind giving a few pointers to a newcomer, please post any
> information that you think might be useful to know.
>
> Thanks
> Jacek Mazurkiewicz

You're not going to be able to generate NTSC because you can't generate a
color signal from 1MHz. You will have to make do with monochrome 60Hz video.
If you are using the LM1881then you must already have some external video
coming in. You'll need to "genlock" the CPU clock to the external video
otherwise the jitter is going to be huge. You have approximately 64
microseconds to put the pixels on each line. Your processor at 1MHz can do
no more than 16 instructions in that time so the horizontal resolution will
be 16 pixels or less. The poor processor won't have time to do anything else
but generate video.

In other words, get a faster processor or an external video generator.
The lowest end generators that I know are written for the old 16f84 PIC
chip. Google for "picdream.zip".
Peter


From: Paul Carpenter on 6 Feb 2005 06:19
On Sunday, in article
<gBjNd.3179$wK.468(a)newsread3.news.atl.earthlink.net>
jack(a)jessmaz.com "Jacek Mazurkiewicz" wrote:

>Can anyone give me an idea as to the bare minimum system requirements for
>generating the picture information for some NTSC video at a very low
>resolution?

Are you creating a video output or a video output overlayed onto an
existing video picture?

If the second does the output still have to produce an output if the
input is missing?

What type of very low resolution information - lines, boxes, characters?

What update rate of information?

Is your information monochrome or colour?

>I'll be working with a small 8085 microcontroller for which I don't yet have
>the exact specifications (it either operates at a 1KHz or 1MHz clock
>speed), and I was wondering if I could somehow use this to generate a
>composite video signal, or if the microprocessor is underpowered for such a
>task.

Even for NTSC getting the line frequency accurately from either of those
frequencies will be difficult.

> I'd need some auxillary circuitry to generate the video sync
>(possibly using an LM1881).

You would only use the LM1881 if you were decoding the syncs from a video
input, it is not a video sync generator.

There are plenty of CPLD free designs for generating NTSC timing patterns.

Look at Altera and other peoples web sites.

> If anyone here who's done something similar
>wouldn't mind giving a few pointers to a newcomer, please post any
>information that you think might be useful to know.

Without knowing answers to the questions above and what space and cost
budgets you have it is pretty meaningless to give many pointers, other
than I would not start from here.

I would start from knowing I could generate the video signals and knowing
what I was trying to output in the way of information. Then consider what
micro and other peripherals I would need.

Video data rates can get a lot faster than most micros depending on the
application.

>Thanks
>Jacek Mazurkiewicz
>

--
Paul Carpenter | paul(a)pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/> PC Services
<http://www.gnuh8.org.uk/> GNU H8 & mailing list info
<http://www.badweb.org.uk/> For those web sites you hate

From: MetalHead on 6 Feb 2005 06:39
Jacek Mazurkiewicz wrote:
> Can anyone give me an idea as to the bare minimum system requirements for
> generating the picture information for some NTSC video at a very low
> resolution?
>
> I'll be working with a small 8085 microcontroller for which I don't yet have
> the exact specifications (it either operates at a 1KHz or 1MHz clock
> speed), and I was wondering if I could somehow use this to generate a
> composite video signal, or if the microprocessor is underpowered for such a
> task. I'd need some auxillary circuitry to generate the video sync
> (possibly using an LM1881). If anyone here who's done something similar
> wouldn't mind giving a few pointers to a newcomer, please post any
> information that you think might be useful to know.

Google on Lancaster "Cheap Video" Don Lancaster wrote a couple of books
called "The Cheap Video Cookbook" and "Son of Cheap Video" covering
exactly what you are trying to do, with a similar CPU back in the 70s or
maybe early 80s. From what I remember, the 808x family was so wasteful
of clock cycles that it was not usable for direct video generation for
text display.

As another poster mentioned, the LM1881 is useful for decoding the sync
signals from an existing video signal. If you wanted to overlay your
video on top of some other signal, it's useful. Otherwise, you could
probably come up with some discrete counters or a timer chip that would
be more useful.


Bob
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