On 9/3/2012 9:22 PM, David Empson wrote:
Charlie<charlieDOTd@verEYEzon.net> wrote:On 9/3/2012 8:15 PM, David Empson wrote:Charlie<charlieDOTd@verEYEzon.net> wrote:On 9/3/2012 3:53 PM, D Finnigan wrote:J. Vernet wrote:As I remember, it's not a drive harware issue but a controler hardware issue... In an USB external floppy, there is an USB controler that do not let the drive being used in 800k (variable rotation speed).It's very likely that the drive can't spin at more than one speed, that the motor is fixed. As far as I know, only Apple computers had variable-speed 3.5" floppy drives. These were manufactured by Sony. The Apple drives used GCR at their lowest level, whereas the IBM drives used MFM.I believe the 3.5" Apple drive can read/write either GCR or MFM if the controller is designed for both. Consider that a normal 3.5" Apple drive when connected to a PC Transformer can read/write 800K ProDOS disks and 720K MSDOS disks that are compatible with IBM clones. Note also that with the 720K disks the floppy drive speed doesn't vary.The Apple 3.5 Drive (800K model) has the variable drive rotation speed as a built-in feature,I agree, but apparently it can be disabled by the controller since the PC Transporter manages to do it for the 720K MFM disks.Are you sure it actually stops the variable rotation speed, as opposed to the controller adjusting the bit cell timing?
Am I sure like would I bet my life on it? No, but I remember listening to the drive while writing a nearly full 720K to an MSDOS disk and hearing no speed changes as it stepped through the tracks. Incidentally, I initially thought the PC Transporter adjusted the bit cell timing so that is why I was surprised when I heard no speed variation.
I no longer have one one of those drives connected to a PC Transporter and it would be a pain to test it again.
I'm in the same boat. My PC Transporter is packed away. I haven't used it in quite a while. Maybe someone in this group has one still hooked up and could give it a test.
The timing signal sent by the Mac to older drives is on the same pin as the Apple II write protect signal (output by the drive), but there is an "Apple II" mode control pin which might be related to this: if the drive was set to operate in Mac mode, it might support the timing control signal, and the PC Transporter's controller could just use fixed timing. (The write protect signal can still be read via a status command.)
I tried to find information several years ago about how the PC Transporter controller worked but there seems to be very little available, at least on the internet. I also tried to look at it from the Apple documentation to see if I could come up with a method using Smartport signals but I couldn't see any way.
If the Apple 3.5 Drive is used with a PC Transporter to access 720K disks, the disk controller on the PC Transporter has to cope with variable bit cell timing depending on which range of tracks are passing under the head. I don't recall whether I used that capability much, but I expect it would be somewhat unreliable for writing, and not too bad for reading.Mine works flawlessly for reading and writing *if* the disks are formatted on a PC or pre-formatted. If they are formatted on the PC Transporter they still work flawlessly if they are used only with the PC Transporter card. The only problem I've found is when a disk is formatted on the PC Transporter some PCs (less than half of those I've tried) have problems with those disks.The formatting may be an issue with the "start of track" position. The Apple 3.5 Drive doesn't provide access to the start of track detector (hole for 5.25" disks, locating notch for 3.5"). If some PC's BIOSes are expecting the tracks to start at the same position, they would not be happy with a staggered start of track position laid down by the Apple 3.5 Drive.
That could be it. I never pursued it after my initial tests with various PCs back in 1992 or 1993. I just made sure I always used a PC to do the formatting and never had a problem after that. I used this method to move a lot of Apple II files to the PC for use in emulators.
Charlie