[Coco] RGB2VGA on Amiga W.I.P.

Zippster zippster278 at gmail.com
Thu Dec 3 12:04:36 EST 2015


By way of explanation…

If you connected the RGB lines directly to the CoCo3 port, your signal
levels would have been too high.

The 82Ω series resistors, in conjunction with the RGB2VGA on-board termination
resistors (82Ω on the boards I produced) form voltage dividers, reducing signal
amplitude to ~ 50 percent, putting it into the adjustment range for the on-board
potentiometer.

I put an oscilloscope on the pins before doing anything, so I knew to do this.
IIRC sync levels were similar to the CoCo3, so I did nothing different there.

Luis mentioned that clocks (PLL settings) may need some adjustment in the FPGA
code for the best picture, but I haven’t had time to explore that yet.

- Ed


> On Dec 3, 2015, at 10:42 AM, Zippster <zippster278 at gmail.com> wrote:
> 
> Dave,
> 
> I recently acquired an MM/1, and I was able to get a pretty decent picture right
> off the bat.  With a little tweaking it should work pretty well.
> 
> This pic is with 82Ω resistors in series between the MM/1 and RGB2VGA board
> on the RGB channels, and the syncs relying on the on-board resistors (connected
> directly to the CoCo3 port).
> 
> <https://drive.google.com/open?id=0B1sgl615FlGncTdsR3pDekJ6QkE <https://drive.google.com/open?id=0B1sgl615FlGncTdsR3pDekJ6QkE>>
> 
> Typically bad cell phone pic, but seems pretty close to what I can make out here…
> 
> <https://drive.google.com/open?id=0B1sgl615FlGndU10TDF4OWlxN3M <https://drive.google.com/open?id=0B1sgl615FlGndU10TDF4OWlxN3M>>
> 
> - Ed
> 
> 
>> On Dec 2, 2015, at 10:11 PM, David Ladd <davidwladd at gmail.com <mailto:davidwladd at gmail.com>> wrote:
>> 
>> I wonder if that might be one of the reasons the RGB2VGA isn't working as I
>> had expected on the MM/1?
>> 
>> +----------+
>> |David Ladd|
>> +----------+
>> 
>> 
>> 
>> 
>> On Wed, Dec 2, 2015 at 4:20 PM, CoCo Demus <retrocanada76 at gmail.com <mailto:retrocanada76 at gmail.com>> wrote:
>> 
>>> It does work, the color resolution is the problem.
>>> 
>>> I will need 1% resistors on it....
>>> 
>>> But the final amiga board is different, I need more pins for more
>>> colours...
>>> 
>>> 
>>> On Wed, Dec 2, 2015 at 12:20 PM, Richard E. Crislip <rcrislip at neo.rr.com <mailto:rcrislip at neo.rr.com>>
>>> wrote:
>>> 
>>>> On Wed, 2 Dec 2015 11:04:39 -0500
>>>> Rich Carreiro <rlcarr at gmail.com <mailto:rlcarr at gmail.com>> wrote:
>>>> 
>>>>> I'll be in for one of those when it's complete!  I've been dying
>>>>> for something like this to be able to connect my Amigas to
>>>>> modern monitors.
>>>>> 
>>>>> On Mon, Nov 30, 2015 at 3:17 AM, CoCo Demus <retrocanada76 at gmail.com <mailto:retrocanada76 at gmail.com>>
>>>>> wrote:
>>>>>> I'm changing the rgb2vga to support Amigas :)
>>>>>> 
>>>>>> 
>>>>>> https://www.youtube.com/watch?v=PGC9veEThMQ <https://www.youtube.com/watch?v=PGC9veEThMQ>
>>>>>> https://www.youtube.com/watch?v=XJ9wT8-_fNg
>>>>>> 
>>>>>> --
>>>>>> Coco mailing list
>>>>>> Coco at maltedmedia.com
>>>>>> https://pairlist5.pair.net/mailman/listinfo/coco
>>>>> 
>>>>> 
>>>>> 
>>>> 
>>>> AT one time there was a Flicker Fixer/Scan Doubler available. I have
>>>> one for my A2000s. It works great with my HP1706 plasma monitors. It's
>>>> too bad the RGB2VGA adapters developed for the CoCo do not work with
>>>> the Ami.
>>>> 
> 



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