[Coco] CM-2 260-3212 color monitor with coco 3?

[Mathieu Bouchard]

You can get 16 colours, but you need more complex conversions to get it. 
If it's much like the CGA, then R,G,B bits are worth 2/3 of the intensity, 
whereas the I bit adds 1/3 grey (all channels). The only exception is the 
hack for the colour brown (for monitors that have it), where G is worth 
only 1/3 when R is on and BI are off (2/3 otherwise). If you digitalise 
the signal, you can find which RGBI bits are the best match, by some 
simple formulas, but if you want to do it with analogue components only, 
it's going to be harder, especially if you have to support the brown hack.

For colour similarity comparisons, there are several possible formulas, 
which all give different importances to the each aspect of the colour. 
Some kind of light blue might be "rounded to" B+I or B+G+I or R+G+B+I or 
B+G depending on how much the formula makes each of those appear similar.

Not using "I" will make the image less contrasted, because of the 2/3 
factor. If you set I always high, the image will have too much brightness, 
and if you set it low, the image will have not enough of it, and can have 
a problem with the brown hack (what was intended to be yellow will be 
brown if you have a monitor that does it... probably the vast majority of 
CGA monitors).


Le 2015-09-19 à 19:26:00, Arthur Flexser a écrit :

> I think you'd get only 8 colors if you interfaced a CM-2 to a CoCo 3.
> The R, G, and B would be either on or off, no in-between, no?
>
> Art
>
> On Sat, Sep 19, 2015 at 5:44 PM, Barry Nelson <
> barry.nelson at amobiledevice.com> wrote:
>
>> According to what I have found the CM-2 appears to use an RGBI interface
>> as opposed to the CoCo 3's analog RGB. RGBI is limited to 16 colors and the
>> signal level is TTL 0 or 5 volts digital. The CoCo 3's RGB line signals are
>> 0 to .7 volts analog. You could construct a circuit to interface the two,
>> but the CoCo 3 can display 64 colors and that monitor can only display 16.
>> I suggest using another solution like my CoCo 3 to HDMI adapter cable to
>> display on a modern display in full color. I am including the CM-2 pinout
>> below.
>>
>> Pin     Name    Description
>> 1       GND     Ground
>> 2       GND     Ground
>> 3       R       Red
>> 4       G       Green
>> 5       B       Blue
>> 6       I       Intensity
>> 7       RES     Reserved
>> 8       HSYNC   Horizontal Sync
>> 9       VSYNC   Vertical Sync
>>
>>
>> > Walter Miraglia walter.miraglia at gmail.com
>> > Just wondering.  I recently acquired a Tandy 1200 HD which came with a
>> CM-2 colour monitor and I am wondering, if I make the appropriate cable,
>> will this monitor work with my COCO3?
>> >
>> > The monitor is at my brother in law's place about 5.5 hour drive away...
>> So wondering if it's worth the drive or if it can wait until thanksgiving
>> in October. (Canadian here eh!)

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