On 03/04/2015 09:03 PM, email@example.com wrote: > On 2015-03-04 20:47, Gerrit Heitsch wrote: > >>> Right - and quite similar to the 6526 in many respects. AFAIR it was >>> something like a 6526 stripped from the timer(s) or so. >> >> The 8520 had a normal timer instead of the RTC the 6526 had. That's >> about it, you can use a 8520 in a C64 if the software doesn't use the >> RTC. > > You mean the TOD? Yes... Looks like they decided they don't need it for the Amiga but another timer/counter couldn't hurt. >> Probably to keep customers from complaining... Especially since the 8521 >> is not quite the same, if I remember right the timer IRQ is one cycle >> late compared to the 6526. Doesn't really matter most of the time, >> unless you use it where the timing is REALLY tight. > > Hm... it's interesting that so many years after one thought he knew > practically everything about the machine - there are still things to > discover again and again :-)) I think there is a debugger that allows you to single step a program which needs such tight timing. The unpatched version is supposed to fail on a 6526A/8521 due to the IRQ or NMI arriving one cycle too late. >> This little tool will detect the CIA (and other chips) you have in your >> box, a 8521 will be listed at '6526A': >> >> http://csdb.dk/release/?id=89406 > > And what if it is a 6526A? Or are all 6526As basically 8521s? Yes. I have a few 6526A-1 (so labeled) and they are detected as '6526'. They also have a datecode before the end of 1986. Which to me, means that all 6526 made 1987 and later are 8521 inside. So far that has checked out. They also run a bit less hot. Gerrit Message was sent through the cbm-hackers mailing listReceived on 2015-03-04 21:00:39
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