[Coco] Is MM/1 to SCART practical?

[David Ladd]

Barry,

Thank you for the information.  I will try the first option to see how that
works.  I first have to order the connector for the SCART and then the
SCART2HDMI converter.

I will reply again once I have gotten time to acquire the items and test it.

+----------+
|David Ladd|
+----------+




On Sun, Aug 23, 2015 at 1:45 AM, Barry Nelson <
barry.nelson at amobiledevice.com> wrote:

>  Ok, if it works with a Tandy CM8 monitor, then that means that the VSync
> timing, the HSync timing, and the video signal voltage are all what a SCART
> device expects to see, so there is hope. However, it also means that if you
> do not have a composite video out, you may have no composite sync signal
> available since the CM8 uses a separate vertical and horizontal sync. To
> make things more complicated, the sync to the CM8 is a positive sync, and
> SCART needs a .7V negative sync. You will need to invert both of the sync
> signals and combine them together and then connect that to pin 20 on the
> SCART connector. This circuit MIGHT work if you add 330 ohm resistor to the
> composite sync output of the circuit to bring the voltage to the proper
> level.
>
> http://www.twobits.com/cga.gif
>
> Issues: The resulting composite sync signal will lack the "front porch"
> and "back porch" plateaus that a composite video signal has. This may
> result in dark or washed out video.
> Solution:  The AD724 IC chip should be able to generate a full composite
> video output for you from the signals you have, as well as an s-video
> signal, which may give you what you need without further conversion as
> s-svideo should provide good resolution at 640x225 480i.
>
> Here is the data sheet on the AD724, which contains a sample circuit to
> convert VGA to s-video which may work for you.
> http://www.farnell.com/datasheets/83869.pdf
>
> You will not need the lower part of the example using an AD8013 chip which
> is to drive a VGA monitor and can simply tie the pin 5 on the AD724 to +5V.
> You will need a 3.579Mhz crystal in addition to the AD724 to attempt this
> solution.
>
> Obviously I have not tested either of these solutions on an MM/1.
>
> On Aug 23, 2015, at 1:18 AM, coco-request at maltedmedia.com wrote:
>
> > Date: Sat, 22 Aug 2015 21:56:00 -0500
> > From: David Ladd <davidwladd at gmail.com>
> > To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> > Subject: Re: [Coco] Is MM/1 to SCART practical?
> > Message-ID:
> >       <CAHW2jkBQufKJKJXHo=
> AkeoB27pzFT5sQzZ4Q3DbUUygRwWqqdA at mail.gmail.com>
> > Content-Type: text/plain; charset=UTF-8
> >
> > Well in this case I don't have to much data from the documentation I have
> > about the video signal stuff.
> >
> > I know I can use a CM-8 monitor on my MM/1 without any problems.  I also
> > use to have a Magnavox monitor I used on the MM/1 and CoCo3.  Sadly the
> > Magnavox died first and then my CM-8 died not long after.
> >
> > So that is one of the reasons I got the RGB2VGA hoping I could use it on
> > both.  The SYNC seems to work on the RGB2VGA, but the colors are so dark
> on
> > the VGA monitor with the MM/1 I can't read the output.
> >
> > The other thing is I don't have the tools to test all this stuff.
> >
> > That is why I was hoping someone out there with a MM/1 might know or have
> > more experiance with this.
>
>
> --
> Coco mailing list
> Coco at maltedmedia.com
> https://pairlist5.pair.net/mailman/listinfo/coco
>