P112

[Fred Cisin]

>>> 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.
As opposed to IBM jumpering both drives as B: and twisting the cable for 
A: (which also provided different control of motor)


>> 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.

>> 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?


> 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!

--
Grumpy Ol' Fred     		cisin at xenosoft.com