[Coco] Color BASIC 1.1 / memory detection

[jon bird]

I've also just had a look through the Color Basic Unravelled document to 
try and figure out how the ram size logic works. It seems there are 2 
bits coming into play from the PIAs:

$FF02, bit #6 "RAM Strobe" (shared with a keyboard column line)
$FF20, bit #2 "RAM Input"

What seems to happen is that RAM Strobe is driven high, then RAM Input 
is checked and if zero, the 4K RAM map is selected. Assuming not, RAM 
Strobe is then driven low and RAM Input checked again. If zero, the 64K 
map is selected and if one, the 16K map is selected. So my guess is that 
it's this that is causing the problem.

However I can't find any schematics online to show what this Ram Strobe 
line actually does. The only ones I can find are from the CoCo Technical 
Reference Manual which don't show this strobe line (presumably a latter 
feature). Does anyone have anything on this?

Rgs,

Jon.

In article 
<CA+LuDccV4+Unb8TO-frQ5sfv01QSxWpsCLOyduobczhQr96stQ at mail.gmail.com>, 
Arthur Flexser <flexser at fiu.edu> writes
>All I can think of is double checking that the jumpers are correctly 
>set.
>Maybe also swap the positions of the RAM chips with one another to see 
>if
>that makes any difference (grasping at straws).  In the process, check 
>to
>make sure none of the RAMs have any bent-under pins.  I would think a 
>bad
>or inoperative RAM would keep the CoCo from booting at all, but who 
>knows?

>Art

On Wed, Feb 18, 2015 at 12:41 PM, jon bird <news at onastick.clara.co.uk>
wrote:

>
>
>
>
> It's definately a 1.1 ROM, the number is stamped on the chip and to be
> sure I pulled the Extended ROM and confirmed it comes up with 1.1.
>
> I also did a quick sense check - POKEing some values above the 16K
> threshold and they all appeared "stuck" at 255. Which suggests that 
the
> SAM has been programmed up for a 16K memory fit.
>
> Rgs,
>
> Jon.
>
> >
> > Art, I have an F-board (chicklet keys) that has both CB & ECB 1.0. 
It was
> > one of the 32k boards that was actually 64k. Oddly, it recognizes as 
32k
> > of ram and not as 16k.
> >
> >
> > Bill Pierce
> > "Today is a good day... I woke up" - Ritchie Havens
> >
> >
> > My Music from the Tandy/Radio Shack Color Computer 2 & 3
> > https://sites.google.com/site/dabarnstudio/
> > Co-Contributor, Co-Editor for CocoPedia
> > http://www.cocopedia.com/wiki/index.php/Main_Page
> > E-Mail: ooogalapasooo at aol.com
> >
> >
> >
> >
> > -----Original Message-----
> > From: Arthur Flexser <flexser at fiu.edu>
> > To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> > Sent: Tue, Feb 17, 2015 6:49 pm
> > Subject: Re: [Coco] Color BASIC 1.1 / memory detection
> >
> >
> > Are you sure that your COLOR BASIC (not Extended Basic) is version 
1.1?
> > You cannot readily detect the Color Basic version with Extended 
Basic
> > installed.  If in doubt, pull the Extended Basic chip and see what 
the
> > startup message reports.  (Though I would think an F-board CoCo 
would
> > indeed have Color Basic 1.1, not 1.0.)
> >
> > Art
> >
> > On Tue, Feb 17, 2015 at 5:14 PM, jon bird 
<news at onastick.clara.co.uk>
> > wrote:
> >
> >> Hi,
> >>
> >> I have just recently resurrected my old Coco 1 (it's a 26-3004A 
variant)
> >> and have been putting it back to an original (working) state (I had 
been
> >> plugging various additional cards & even a Dragon ROM into it at 
some
> >> point).
> >>
> >> The info I can find on this version of the CoCo was that it was 
shipped
> >> with 16K RAM, Color BASIC. It had an Extended BASIC 1.1 ROM fitted 
many
> >> years ago and as part of my various "upgrades", replaced the 16K 
RAM
> >> chips
> >> with 4164 DRAMs & also switched over the jumpers.
> >>
> >> What I am finding though is that having restored the original Color
> >> BASIC
> >> 1.1 ROM, it is only reporting a 16K memory fit. I'm pretty sure 
that
> >> when I
> >> had the Dragon ROM fitted, it could access the full 32K (and I'm 
also
> >> fairly sure I had OS9 running on it as well which suggests the full 
64K
> >> is
> >> accessible). So this seems to be a feature of the BASIC ROM.
> >>
> >> I did come across this article from the archive:
> >>
> >>
> 
http://coco.maltedmedia.narkive.com/2DM5LvJ2/color-basic-1-0-1-2-differen
> >> ces
> >>
> >> which backs up some other information I found that the original 1.0 
ROM
> >> did not support >16K memory fit but that the 1.1 ROMs do.
> >>
> >> Can anyone shed some light on this behaviour?
> >>
> >> Cheers,
> >>
> >>
> >> Jon.
> >>
> >> --
> >> == jon bird - software engineer
> >> == <reply to address _may_ be invalid, real mail below>
> >> == <reduce rsi, stop using the shift key>
> >> == posted as: news 'at' onastick 'dot' clara.co.uk
> >>
> >>
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>
> == mailto:jon at onasticksoftware.co.uk - in real life jon bird
> ==  http://www.onasticksoftware.co.uk - stuff, on-a-stick
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-- 
== jon bird - software engineer
== <reply to address _may_ be invalid, real mail below>
== <reduce rsi, stop using the shift key>
== posted as: news 'at' onastick 'dot' clara.co.uk