Date: Sat, 13 Sep 1997 01:22:07 -0500 From: dkelly@hiwaay.net To: Greg Lehey <grog@lemis.com> Cc: Robert Clark <ROBERTC@PII.COM>, questions@FreeBSD.ORG Subject: Re: Floppy Trouble / Cable Select. Message-ID: <199709130622.BAA18769@nospam.hiwaay.net> In-Reply-To: Message from Greg Lehey <grog@lemis.com> of "Sat, 13 Sep 1997 10:11:32 %2B0930." <19970913101132.23596@lemis.com>
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Greg Lehey writes: > > On Fri, Sep 12, 1997 at 09:05:16AM -0700, Robert Clark wrote: > > Scenario: > > > > You have two floppy drives in your PC. For some reason, you would like > > to swap A: & B:. Your BIOS won't do it. > > > > You reach into the case, and move both drive select jumpers from 0 to 1. > > (Or is it the opposite?) > > No. From 1 to 2. I've seen floppy drives marked 0,1,2,3 and others 1,2,3,4. It just depends. Is this saying "From 1st to 2nd" or "From 2nd to 3rd"? See below. > > Now drives A: & B: are swapped. > > The controller can address four units, 0 to 3. It outputs the drive > number in binary on two drive select lines. You all know what a > floppy cable looks like: it's a kludge, they've torn the flat cable > apart and swapped the drive select lines. This means that you don't > need to set the jumpers on the floppy itself. They're both set to 1. > The system addresses /dev/fd1 as unit 1 and /dev/fd0 as unit 2. The > swap in the cable swaps the two address lines, so the second floppy > responds to address line 1 (the '2' bit) instead of address line 0 > (the '1') bit. > > > Problem: Things get weird. Some systems don't like this arrangement. > > They can't tell. It's the same as swapping the cables. Of course, > it's important to change both drives. I don't think its the same a swapping the cables. IBM came up with a weird cable when they opted to put a twist in the cable and jumpered all floppy drives as the 2nd drive (B: to some people). Back in the Good Old Days, not all floppy drives were sold to the IBM market. Back then drives didn't ship from the factory as B:. Even so, there were compatibility issues. Some systems for performance spun all floppies when one was accessed. They used a MOTOR signal on the cable. There might also be a head load signal. Some drives I've seen were sensitive to the motor signal arriving before or after the drive select. Get the signals in the wrong order and the drive doesn't spin. Am pretty sure the motor signal is one of the wires that gets twisted in IBM's cable. Am not surprised simply changing the drive's ID doesn't swap A: and B:. I see my BIOS has an option to swap the drives. It could work with FreeBSD if it was a hardware feature of the FDC. Don't know, haven't tried it. -- David Kelly N4HHE, dkelly@hiwaay.net ===================================================================== The human mind ordinarily operates at only ten percent of its capacity -- the rest is overhead for the operating system.
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