Reading about all those circuit board and chip revisions, I had to think about when the HMOS version of the C64 was originally created or planned. There are several strange facts when I look at the release dates of the other 8bit machines and compare it to several C64 facts: 1984: 264 series released, HMOS-1 or HMOS-2 1985: 128 released, HMOS-2 1986: C64C released, NMOS, but the case is clearly prepared to mount the HMOS-2 equipped C64E board. Not only that, the case is optimized for the C64E board, the C64B doesn't mount too well in there. 1987: finally, the HMOS-2 C64E board is released. The list of video chip type numbers suggests something else: 8562 C64E VIC-II NTSC 8563 C128 VDC 8564 C128 VIC-II NTSC 8565 C64E VIC-II PAL 8566 C128 VIC-II PAL 8567 never seen this, does it exist? 8568 C128CR/DCR VDC Is it just a coincidence, or why do the C64 chips have lower numbers than the C128 chips, if they actually were introduced later? Also, PAL versions have higher numbers than NTSC versions, but this is normal. So I come to the conclusion, that CBM was already working on redesigning the C64 chips when they decided to push out the 128. C64 redesign was delayed until the 128 was finished and even then CBM had to fight further difficulties, e.g. the redesign of the CIA chip, which failed more than once. Evidence is the only shortly used 8521 CIA, that only appeared in some C64 and C128 machines from 1986, and only in one of the two CIA sockets. Something must be wrong with that chip ... The 6526 chips that were manufactured after 1987 must be other redesigned versions, because their IRQ timing is one cycle off, which leads to problems with certain software. The 8521 didn't have that problem. I also take the C64B3 board as a desperate attempt to cut down costs by using the new memory chips while the C64E board was waiting to be equipped with a working chipset. Nicolas - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail email@example.com.
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