> On 2019-08-27, at 21:43, Spiro Trikaliotis <ml-cbmhackers_at_trikaliotis.net> wrote: > >>> ... which is, essentially, what the (infamous) 5710 chip in inside the >>> 1571CR (128DCR) does. >> >> I (again…) forgot what was the main problem with the DCR that it got >> so much negativity. Was it because of this chip and potentially >> related incompatibility? > > IIRC, the serial bus was "compatible enough" and should not do much > harm. But, to be sure, I would have to re-check. I am currently lacking > time for this. > > The biggest issue was the WD177x replacement part of the 5710, that was > very different. So, (not only) because of this, the Floppy ROM of the > 1571CR differs essentially from the 1571, so any program that uses jump > addresses in the $8000-$BFFF area is likely to break, as is any program > that tries to access the WD177x directly. > > From the ROM code, I can see that even the order of the accesses of the > registers is different. I see. If they're so different, then the ROM needs to be highly different, with all issues that follow it. What we did for DD4 was to first make the chip fully compatible so that a "superset" can be built on top what was working well. Only once existing, original DOS and programs ran all correct, new features were implemented. But yeah - if one doesn't live off these things he can afford to do it "right" (and usually long, unfortunately). -- SD!Received on 2020-05-29 22:54:57
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