On 04/08/2018 02:11 PM, Fred Cisin wrote: >>>> I do have to admit that I find it hard to believe that the cable to >>>> the >>>> floppy can actually make a difference. >>> A minor point, . . . >>> On 5150/5160/5170, the SECOND drive is a straight cable, FIRST drive >>> is crossed. Thus, drive A: is at the end of the cable, B: is in the >>> middle of the cable. > > On Sun, 8 Apr 2018, Bill Gunshannon via cctalk wrote: >> Yeah, knew that from other systems. IBM really screwed that up. >> Should have left it the way it was and have people set the Drive Select >> themselves. > > Yep! > IBM didn't think that users could be trusted to get that right. > Or at least Computerland couldn't be trusted to get it right. > > Radio Shack used a different approach to drive select by cable instead > of making use of the well documented drive select on the drive. > Radio shack jumpered all drive selects on on the drive, and pulled > pins in the cable.
Or, as in the case of some of the 1000 series (I had a TX my father an SL) punch holes in the cable to break the connection. > As opposed to IBM jumpering both drives as B: and twisting the cable > for A: (which also provided different control of motor) Which also limited you to two drives. > > >>> IF that is correct, then your first drie is straight through. That >>> also means that an unkeyed cable can be reversed, as one more to try. >> Reversed cable will result in the drive being active constantly. >> Easily noted by the LED being on constant and the drive running. > > I meant reversing BOTH ends, end for end, giving same wiring. > in case some lines of the cable are flaky. Too many different cable for that to be likely. > >>> I did not see any mention of the disk format. >>> If it is 512 bytes per sector MFM, with sequential sector numbering, >>> then even USB drives should work for making disks. >>> A different sector size, or even numbering sectors from 0, would be >>> problematic for some USB drives. >> >> I have no idea of the format. I got the images and rawrite.exe and >> told the computer to make them. They were unusable when I used >> a USB External floppy but worked fine when I used a real internal >> floppy. > > Since they mimiced the 5150 cabling, I was hoping that maybe they had > made the format similar, or at least the same physical format. > There are more efficient physical formats (using 1024 bytes per sector > easily gives you 400k/800K instead of 360K/720K) > > >> I need to get the systems running before I start playing with reading >> and writing weird formats. But that is coming. > > Should be fun. > Is the FDC a 765 variant? > or a WD 179x variant? SMC 37C651. Supports 500 Kb/s, 300 Kb/s and 250 Kb/s Data Rates. Something else we lost with the PC. > > >> As a side note, I did get the system to boot and run from my floppy >> emulator with a USB stick. Have to boot twice. First time you get >> the unrecognized format error second time boots fine. Interesting. >> Good to know for when I am testing on other systems as well. >> Small steps, but advancing, just the same. > > Good luck! Thanks. bill