Bill Gunshannon bill.gunshannon at hotmail.com
Sun Apr 8 12:52:41 CDT 2018

On 04/08/2018 01:34 PM, Fred Cisin via cctalk wrote:
> On Sun, 8 Apr 2018, Bill Gunshannon via cctalk 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.

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

> The P112 manual
> https://661.org/p112/files/p112-doc.pdf   Page 10
> calls for the reverse, with FIRST drive before the twist, SECOND drive 
> after the twist.
> 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.

> Termination is rarely an issue with 3.5 inch drives, and not usually 
> the problem with 5.25".   5.25" has explicit provision for 
> termination, but wrong termination usually results in slightly less 
> reliability, not often a total failure to read.

Just using 3.5" at the moment.

> 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

I need to get the systems running before I start playing with reading
and writing weird formats.  But that is coming.

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.


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