On 03/05/2015 07:36 PM, Jim Brain wrote: > On 3/5/2015 12:25 PM, Gerrit Heitsch wrote: >> >> Well, the way it looks with MOS means that the lower last number is >> the chip that was done first, just like the 6520 and the 6522. >> >> So they had that 6526 in NMOS and when the Amiga design came around >> ('85), they wanted a CIA for it as well but decided against the >> TOD/RTC from the original design, probably wanting the plain counter >> instead. > This is what makes no sense. > > Hey, we're building a new PC. Let's see, we have a steady source of CIA > chips we could use. Uh, no, let's go to *ALL* the trouble to tape out a > new IC, drop the TOD clock, go to a new process, and test it all and run > through 4 revs just to get it working. > > That is nuts. The 6526 variant was speced at 2MHz, just pull it out of > the parts bin and use it. Why go to all the trouble to create a new > IC. That makes no sense at all. The 8520 runs at about 700 kHz (E-clock from the 68000 which is, as far as I know CLOCK/10) in the Amiga, so speed is not the issue. I can only imagine that they didn't need the TOD/RTC but thought a plain counter would be more useful. Remember, Commodore made a lot of different chips just because they could... Why a special CPU for the 264 series and the C128 instead of just using a different bond out of the 6510? The 8500 is the 6510 in HMOS-II and, judging from the number, the earlier design than the 8501 and 8502. Or why the 6523 and later the 6525 (6523 with IRQs)? And then all the 77xx-TTL replacements... Or the 6529... Gerrit Message was sent through the cbm-hackers mailing listReceived on 2015-03-05 20:00:07
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