[Coco] GBS-8200 RGB to VGA

[Barry Nelson]

That solution may "work" but I strongly suggest adding at least 100 ohm resistors to pins 8 and 9 before tying them together, otherwise when pin 8 is high and pin 9 is low or pin 9 is high and pin 8 is low you are creating a short circuit across the hsync and vsync outputs of the CoCo 3. I checked the CoCo 3 schematic and there is no protection on those outputs, they are tied directly to the output of an inverter chip so if those outputs are shorted out you could eventually burn out that chip. At least they are not wired directly to the GIME chip.

On Sep 4, 2015, at 1:18 AM, coco-request at maltedmedia.com wrote:

> Date: Thu, 3 Sep 2015 21:29:50 -0500
> From: George Ramsower <georgera at gvtc.com>
> To: coco at maltedmedia.com
> Subject: Re: [Coco] GBS-8200 RGB to VGA
> Message-ID: <55E9021E.6030600 at gvtc.com>
> Content-Type: text/plain; charset=utf-8; format=flowed
> 
>  Kandur,
> 
>  I think I may have never found this out on my own. You are correct, it 
> is quite simple and effective. I, for one, am quite pleased with the 
> outcome, although the photos were not possible to figure out until I 
> found the typed instructions in the third image.
>  You are right about keeping it simple, silly. KISS.
>  Thanks, BIG help on this problem.
> George R.
> 
> On 9/3/2015 7:42 PM, Kandur wrote:
>> I have mine working fine in OS-9, with 80 character display,
>> without using any additional chips. Take a look at it,
>> 
>> http://qdv.pw/coco/?p=317
>> 
>> Kandur
>> 
>> Wednesday, September 2, 2015, 11:46:33 PM, you wrote:
>>> I have had problems feeding that sync signal to anything except a CM8, even
>>> after fixing the polarity and boosting the signal. For some reason the sync on
>>> the NTSC video works better. Anyway, try the 7402 and let me know if it works for this.
>>> coco-request at maltedmedia.com
>>>> Date: Wed, 2 Sep 2015 21:53:54 -0500
>>>> From: George Ramsower <georgera at gvtc.com>
>>>> coco at maltedmedia.com
>>>> Subject: Re: [Coco] GBS-8200 RGB to VGA
>>>> Message-ID: <55E7B642.2070102 at gvtc.com>
>>>> Content-Type: text/plain; charset=windows-1252; format=flowed
>> 
>> 
>>>> about it.
>> 
>>>> 7402 is all that is needed.
>>>> George R.