[Coco] MC6847 VGA (FPGA) Project underway...

[Brendan Donahe]

Art,

That's good input.  Although I had ADOS, "back in the day" I didn't have a
machine with a 6847T1 and wasn't aware of the re-purposing of SG6 for
lowercase.

Curtis,

I noticed that the characters shifted up and left by a single pixel in the
newer font set.  I hope we will be able to select between them to avoid
this problem - Steve implemented both of them when we started this project
and I can switch between them on the prototype board.  To be sure, it
sounds like I'll have to try out Protectors II.

Thanks,
Brendan

On Thu, May 26, 2016 at 1:55 PM, L. Curtis Boyle <curtisboyle at sasktel.net>
wrote:

> That is the safest way, although it will (partially) break anything that
> used the text characters intermixed between scanlines, as the characters
> have shifted within the character cell somewhat, and a few characters have
> changed (the main one affect by this would be Synapse Software’s Protectors
> II, and the mixed text characters they used to do the waving people. You
> will also notice some games that did scores, etc. with regular text to the
> exact height of the text character (not including extra, unused space on
> the top and bottom) will also be cut off somewhat, if you exclusively use
> the Coco 2B/Coco 3 style lowercase VDG mode.
>
> L. Curtis Boyle
> curtisboyle at sasktel.net
>
> TRS-80 Color Computer Games website
> http://www.lcurtisboyle.com/nitros9/coco_game_list.html
>
>
>
> > On May 26, 2016, at 12:48 PM, Arthur Flexser <flexser at fiu.edu> wrote:
> >
> > What Darren says corresponds with my recollection as well, although I did
> > not have an explanation for it.  You get vertical colored stripes but
> there
> > are black gaps between them.  Also, no ability to mix in letters, a
> useful
> > feature of other semigraphics modes.  When the CoCo 2B with the real
> > lowercase came out, with SG6 eliminated, I heard of zero complaints of
> > software that wouldn't work.  (I was selling ADOS at the time, which
> could
> > be configured to default to the real lowercase, so I was in a position to
> > hear such complaints.)  SG6 is a completely useless mode.  If you are
> going
> > to put in lowercase characters, I think you should substitute this mode
> for
> > SG6 for compatibility with CoCo 2B and CoCo 3 software that uses the real
> > lowercase.  That is, have the real lowercase mode turned on by what would
> > previously have turned on SG6, as is the case with the CoCo 2B and the
> CoCo
> > 3.
> >
> > Art
> >
> > On Thu, May 26, 2016 at 12:22 PM, Brendan Donahe <brendan at polylith.com>
> > wrote:
> >
> >> Thanks, Darren - that explains some of the things I have seen in SG6
> mode.
> >>
> >> The Mini-MPI looks great, Ed!
> >>
> >> Brendan
> >>
> >>
> >>
> >> On Thu, May 26, 2016 at 11:18 AM, Darren A <mechacoco at gmail.com> wrote:
> >>
> >>> On Thu, May 26, 2016 at 7:41 AM, Brendan Donahe wrote:
> >>>
> >>>>
> >>>> I had the understanding that SG6 didn't work right on the CoCo, too,
> >>>> however, it looks to me like it can on some systems, and I don't want
> >> to
> >>>> exclude the Dragon or MC-10.  (Also, I could swear that I saw 6 pixels
> >>> per
> >>>> character block in one of Steve Spiller's tests of SG6 on my CoCo 2.
> >> Can
> >>>> someone describe clearly what is broken?  Is it, perhaps, a limited
> >>> number
> >>>> of colors, caused by what pins are tied together on the board?  I
> >>> obviously
> >>>> have not spent much time investigating this yet...)
> >>>>
> >>>
> >>>
> >>> The problem with SG6 is that all 256 byte values are used to produce
> >>> graphics characters in that mode. But because the CoCo, Dragon and
> MC-10
> >>> all have the A/S pin hard-wired to data line D7, you can only use
> values
> >>> 128-255, eliminating half of the available colors in each color set.
> Byte
> >>> values 0-127 will give you the External Character ROM mode. Since there
> >> is
> >>> no external character ROM you end up with vertically striped characters
> >>> corresponding to the byte's bit pattern.
> >>>
> >>> - Darren
> >>>
> >>> --
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> >>> Coco at maltedmedia.com
> >>> https://pairlist5.pair.net/mailman/listinfo/coco
> >>>
> >>
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> >>
> >
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>
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