[Coco] (Probably stupid and newbie-ish) CoCo hardware question

[Arthur Flexser]

Legality may have been the motivating factor, but I doubt they'd have
achieved nearly as good compatibility with prior software had they
used another scheme.  All you need to do is switch the ROMs in and
Super Extended Basic vanishes and you have a configuration that is
extremely close to what the software expects from a CoCo 1/2.

90+ percent of the incompatibilities that do exist are probably due to
putting a bunch of new secondary vectors just below $FF00, a
completely independent design decision.  And, come to think of it,
probably a dubious one.  Can anybody tell me why these secondary
vectors were actually needed?   They certainly messed up compatibility
with a lot of software that rewrote bytes at the top of memory in
order to test memory size.

Incidentally, the original Microsoft ROM code actually was changed in
some minor ways, such as in redefining what DLOAD did, which if I'm
remembering correctly was not done by patching.  (DLOAD does the same
thing on a CoCo 3 as pressing reset.)

Art

On Wed, Jun 27, 2012 at 8:39 PM, Boisy G. Pitre <boisy at tee-boy.com> wrote:
> Take it from an ex-Microware engineer and employee who questioned the source directly.
>
> Mark Hawkins and I had a conversation about the CoCo 3 project years ago.  He told me then, personally and specifically, that ROM to RAM and subsequent patching was the approach that they (Microware) took in '86 to avoid any legal entanglements with Microsoft.  I don't know if Tandy advised them to do it, or if Microware made the suggestion, but legality was the motivating factor for the approach that was taken.
>
> What we need is a book that brings all of this information in... something I've been working off and on for a long time....
>
> Best Regards,
> Boisy G. Pitre
>
> Join our forums at http://www.tee-boy.com/forums/ to exchange ideas and information with other WeatherSnoop enthusiasts.
>
>
>
>
> On Jun 27, 2012, at 7:24 PM, Frank Swygert wrote:
>
>> I'm going out on a limb here... I know it for a fact. I just can't remember the exact source. I'm sure it was one of the Microware guys who modified the system ultimately, but I got the info second hand from an article in some magazine or other... I think. Could have been an on-line article, but I think it was actually in a Rainbow article sometime after the CC3 was released... maybe an interview with one or more of the Microware guys involved? I can't recall exactly where I got the info, which is why I say I'm going out on a limb by saying it's a fact. If Tandy had the rights to mod the MS code, they'd have done it rather than use a patch system though. Would have been cheaper to do it that way, I'd think. I believe the CC3 had two ROM chips, ECB and SECB, or were they both burned in different banks of the same chip? I don't remember...
>>
>> -------------
>> Date: Tue, 26 Jun 2012 14:42:08 -0400
>> From: Arthur Flexser<flexser at fiu.edu>
>>
>> Frank, that's the first time I've heard that explanation for why the
>> CoCo 3 runs in all-RAM mode.  (That Tandy had rights to use, but not
>> modify, the Microsoft ROMs.)  It seems very plausible to me.  Do you
>> know this for a fact, or is it just a reasonable conjecture?
>>
>> --
>> Frank Swygert
>> Editor - American Motors Cars Magazine
>> www.amc-mag.com
>>
>>
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