I have compared the 8280 chips in Bo Zimmerman's list to the 8250 chips listed in the 8050/8250 service manual on funet. 2/3 of the chips are the same. The 8250 chips that are not in the 8280 can all be found on page 3 of schematic 80800001. This is the schematic of the drive control functions; data R/W, stepper & motor control. It appears that the DOS part of the 8280 is the same as the 8250, but the controller part is completely different. There is no controller chip in the 8280 list. There is also no 6530 or 6520, which function as the controller chip in the other IEEE drives. There is a second 6502 and a 128x8 byte RAM chip(68A10) which could be it's zero page memory. There is also a 74LS244 octal line driver/buffer/transceiver that could act as an output port for data written to the mechanism, but there is no shift register to convert parallel to serial data. There is a WD2143-03 four phase clock generator that presumably produces the necessary timing signals, but everything else must be done with standard logic chips. The 2K ROM appears to be a controller ROM. When compared to the GCR ROM, there are only 8 bytes the same, exactly what you would expext from pure chance. When compared to the other IEEE drive controller ROMs, about half the locations match. This is the usual result when comparing controller ROMs from different versions of DOS. The real test would be to compare it to the DOS 3.0 controller ROMs in the 9060 or 9090 hard drives, but we do not have those ROM files. - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail cbm-hackers-request@dot.tcm.hut.fi.
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