[Coco] RGB to XGA (Bruce Borer)

[Bruce Borer]

Hi Andrew,
    After reading your comments about 225 lines I searched and found this
site
BASIC225 <https://nickmarentes.com/ProjectArchive/basic225.html>
This will help me support 192, 200 and 225 lines.  But that will be in the
new year.

Bruce

On Wed, Dec 24, 2025 at 1:51 AM Bruce Borer <brucep.borer at gmail.com> wrote:

> Hi Andrew,
>     This is more information than I was aware the CoCo3 could produce
> My converter supports WIDTH 32, 40 and 80 because by supporting
> WIDTH 80 the others are a subset.
>    Tell me more how the CoCo3 can produce 225 lines and I will work on
> supporting it.  May be supporting 400 pixels by 225 lines then all other
> modes would be a subset.  I believe the current hardware (video RAM)
> can support it and the software can easily be changed to also support
> the extra lines.
>
>     Where can I get information on 225 lines of video from the CoCo3?
>
> Bruce
>
> On Wed, Dec 24, 2025 at 12:37 AM Andrew Ayers <keeper63 at cox.net> wrote:
>
>> Hello Bruce,
>>
>> I was trying to point out that there are other GIME graphics modes which
>> it can display (and they can be used, but there isn't many applications
>> that do - I think the majority of apps that do are recently written
>> (post-1992ish?) games); also, the 225-line mode (and the others that
>> exist, I forget their values).
>>
>> I was just asking if you had tested all of those with your converter,
>> since you mentioned only the 192-line mode, for instance? The tweaks to
>> get the higher number of lines were something that was well known "back
>> in the day", so there might (or is?) more software that uses them
>> (versus the alternate GIME graphics modes, which while likely known,
>> were either little exploited, or not at all).
>>
>> And the "256-color" artifacting mode is just something from the
>> composite output that - while "sorta-kinda" was known about by some back
>> then, it wasn't widely published about; I know of one publication about
>> it in Hot Coco - but I've not found anything about it in the Rainbow;
>> someone who worked for - I think Sundog? - supposedly knew about it, but
>> for some reason, it was never known or experimented with, that I know
>> of, by other users or developers (a curious tale which we'll likely
>> never know the reasons why - I surmise that people were so enamored by
>> the more colorful modes, and RGB output, that for some reason it never
>> occurred to them to play around with the 640x192x4 color mode with the 4
>> grayscales and do the same "magic" as the PMODE4 screen).
>>
>> The CoCo 3 has limited SG modes; SG4 and I think SG12/24 (???) - I'm not
>> sure; the former is of course fully supported, while the latter two (or
>> one?), like the CoCo 2, requires some special "POKES" and such to
>> access, and for speed you need to use ML. Also, unlike the CoCo 2 VDG
>> modes, it can't mix text with the semigraphics.
>>
>> Because you say your adapter works in WIDTH32, those modes should be ok,
>> I would think - but testing them could reveal differently.
>>
>> Of the links I posted to you, the 3D printed "enclosure" should be of
>> interest, since it was designed for a video mod primarily, but also that
>> it fits inside the recess you spoke of; in theory it could make your
>> adapter a more "commercial" kind of device - but since there aren't any
>> design files, you'd either have to somehow convert it back into those
>> (not sure if there are any tools to go from an STL to some other 3D
>> editor or CAD formats) - or re-engineer it entirely.
>>
>> Ultimately, I was just wondering if you had tested all the known
>> graphics modes the CoCo 3 can work in, or just a limited subset, and if
>> the latter...perhaps trying those other modes and/or adapting your
>> hardware and/or code to support them might be of interest to you.
>>
>> Andrew L. Ayers
>> Glendale, Arizona
>> phoenixgarage.org
>> github.com/andrew-ayers
>>
>> On 12/23/25 9:26 PM, Bruce Borer wrote:
>> > Hi Andrew,
>> >     You seem to be asking about changes to the CoCo itself.  My
>> > converter just displays what the CoCo3 produces, including making WIDTH
>> > 80 readable on readily available monitors.
>> >
>> > Bruce
>>
>