Re: MFM drive gone nuts

----- Original Message ----- 
From: <silverdr@wfmh.org.pl>
To: <cbm-hackers@musoftware.de>
Sent: Sunday, July 20, 2014 8:51 AM
Subject: Re: MFM drive gone nuts


On 2014-07-20 at 12:58:03, Michał Pleban (lists@michau.name) wrote:

> > On PC controllers, they should always be jumpered as DS1, and the cable
> > twist makes the drive on the end (which should be terminated) drive 0.
> > (only ONE DS jumper should be enabled at any one time.
>
> That got me thinking. The drive is jumpered as the drive 0, but the
> cable is NOT twisted. Does it mean that the drive should be jumpered as
> drive 1?

I think we don't know that. Twisting cables instead of setting drives' DSx
selectors appropriately is one of the utterly sick PC "inventions". A kind
of PC-crap approach to the standard. CBM usually tried to be more sane in
how they used/implemented standards (Remember? We always admired CBM's
engineering teams and their achievements. The same can not be said about
other divisions. Especially after Tramiel went..). Meaning it might very
much be that there is no need for any "cut'n twist cable" stupidity in this
machine. But we can't be sure. Especially that it's not a production
machine. I guess the best is to try.

--
SD!

----- Reply: -----

I really get a little annoyed sometimes by this de rigeur childish
IBM-bashing, especially when the 'basher' doesn't seem to understand what
he's calling "utterly sick", "PC-crap", "stupidity" etc.

First of all, the twisted cable is only required with a PC-compatible
*FLOPPY* drive controller; hard disks can be (and usually are) connected the
'standard' way with straight-through cables and drive selected with one of
four possible jumpers/switches.

Note that if you do choose to use a twisted HD cable (which allows
moving/swapping drives without having to worry about changing DS settings)
the 'twisted' wires are *not* the same as in a floppy cable.

Also note that this technique of Cable-Selecting drives by their _position
on the cable_ that you find so "stupid" (as opposed to having to set arcane
switches/jumpers on each drive) was also used with IDE drives, especially on
the later boards using 80-conductor cables.

As to the "utterly sick" and "stupid" twisted *floppy* cable, not only did
it allow installing/swapping drives without changing any jumpers or
switches, but it was an IMO ingenious way around the issue that most drives 
of
the day had no provision for individually controlling the drive motors; 
select one drive and its motor and all other drives on the bus would spin 
(with unnecessary wear on disks and drives and wasting considerable power).

The "PC-crap"py twist allowed using the unused drive 3 and 4 select lines to
individually control the motors in drives 1 and 2.

m


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