Kaypro System disks?

On 8 Jul 2009 at 11:27, Christian Corti wrote: Your 1988 PC is too late.. I did not say that the 765 needs the IDAM, but that it was "blind" during the IDAM period. The original 16-64K 5150 was equipped with an Intel 8272 FDC, which is essentially Intel's rebranding of the NEC uPD765. I still have the FDC from my 5150 and there it is--marked "P8272". Let's go to the datasheet for the 8272--I refer you to the 1984 Intel "Microprocessor and Peripheral Handbook", page 6-226. Look at the section labeled "8272A Enhancements": "On the 8272A, after detecting the index Pulse, the VCO Sync output stays low for a shorter period of time. See figure 4A." On the 8272A, the time given for the length of the VCO sync is 527 uS- -I seem to recall (but I can check) that it was over 1 mS on the 8272. The long VCO sync period was a headache for reading 10 sector formats on the original 5150. Note that it's not a problem for disks formatted on the PC--the 8272/uPD765 always writes an IDAM--there's no way to suppress it. But that's not true of the WD17xx/27xx floppy controllers. One can just about put whatever one wants down as a track format. Indeed, in WD179x datasheet (page 18) it is stated that "In addition, the Index Address Mark is not required for operation by the WD179x." Not all versions of the Kaypro format fail on the original 8272/uPD765, but enough do to warrant Media Master's caution. 10x512 sector Cromemco diskettes are perhaps the worst in this regard; indeed many can't be read without "tweaking" even on controllers equipped with the 8272A/765AC parts. As far as the head ID being the cause for the statement, I don't think that was the issue. There are other formats that involve non- standard head ID fields (e.g. Xerox 16-8 and 820) that woiuld have tripped Media Master up but IIRC didn't. Since one had to lay out the whole track to be formatted on the WD179x chips, it was a shortcut to use the same layout for both sides of a diskette and so was quite common. --Chuck