landry@enginr.dec.com (01/04/90)
I read most of the messages on using generic drives with the ST and didn't expect any problems but . . . I'm adding a Toshiba ND-352TH-A also known as FDD4216G0D as a second floppy. If I leave the media change diode (pin 34 ---|<|--- pin 28) out, everything works fine, except of course media change is not detected. With the diode, once the disk is removed once it always appears write protected. So I looked at the signals (only have a logic probe at home - but it's a good one :-) ). The "no media change" condition is indicated by a "high" on pin 34 (jumper selected for this function) all the time. "Media change" is indicated by that pin toggling with no drive select or constant low when the drive is selected. It seems that the only way I can get "no media change" is to power up the new drive with a disk inserted AND then reboot the ST. Once the disk is removed once, "media change" is always indicated. So, my questions are: 1) What is the media change signal really supposed to do? I guess that really is, what does Atari expect it to do? 2) What is supposed to reset it from the "media change" condition? 3) Is it possible to use this drive with the ST? thanks chris
clf3678@ultb.isc.rit.edu (C.L. Freemesser) (01/05/90)
> I read most of the messages on using generic drives with the ST and > didn't expect any problems but . . . > > I'm adding a Toshiba ND-352TH-A also known as FDD4216G0D as a > second floppy. If I leave the media change diode > (pin 34 ---|<|--- pin 28) out, everything works fine, except of > course media change is not detected. With the diode, once the disk > is removed once it always appears write protected. > This is a common problem with home-brew drives. There are a number of solutions to this problem: 1) Get TOS 1.4. It fixes the problem for good by forcing a re-read of the disk every time it is accessed. 2) Run a jumper between pins 2 and 28 of your drive. On some drives, this will solve the problem. However, the ND-352 isn't one of these. The signal becomes too weak. TO boost it, use a 74HC14 buffer chip. 3) Install a momentary on switch between pins 2 and 28. When you insert a disk, hold the button down, and it will detect the media change, and not screw up write protect. This is somewhat clunky, but it works. > 1) What is the media change signal really supposed to do? > I guess that really is, what does Atari expect it to do? > 2) What is supposed to reset it from the "media change" > condition? The ST hooks these two lines together (pins 2 and 28). As I said before, just hook em together. > 3) Is it possible to use this drive with the ST? Yes, very possible. Chris Freemesser, Rochester Institute of Technology :BITNET:%clf3678@RITVAX ||| ____________ :GEnie: C.FREEMESSER ||| /___ / (and 8-bit too!) :USENET: clf3678@rit.isc / | \ ______/ / : .edu Call the A.C.O.R.N BBS (716)436-3078, 300/1200 baud :<-or my BBS
exspes@gdr.bath.ac.uk (P E Smee) (01/05/90)
In article <1856@ultb.isc.rit.edu> clf3678@ultb.isc.rit.edu (C.L. Freemesser) writes: >> >> I'm adding a Toshiba ND-352TH-A also known as FDD4216G0D as a >> second floppy. If I leave the media change diode >> (pin 34 ---|<|--- pin 28) out, everything works fine, except of >> course media change is not detected. With the diode, once the disk >> is removed once it always appears write protected. >> >> 1) What is the media change signal really supposed to do? >> I guess that really is, what does Atari expect it to do? The ST does NOT use the 'media change' signal (aka the 'disk inserted') signal. It expects the 'write protect' signal to be asserted when a disk is removed and uses that to decide whether the disk might have been swapped. Chinon drive mechs (some models) had this problem. The cure for the affected Chinon mechs (which I'll describe in case it helps find a fix) is to open the disk drive and have a look around. (KEEP YOUR GREASY FINGERS AWAY FROM THE DISK HEADS AND ACTUATOR.) The mechs had two adjacent and identical push switches. One was the write protect switch, pressed down when you insert a disk with the protect window closed. Next to it was the 'disk present' switch, pressed down when a disk is inserted. (You can see which is which by putting a disk in while you've got the mech opened up.) The cure was to put a jumper across the pins of the 'disk present' switch, so that the drive always thinks there is a disk in. Those mechs only report 'write protect' if there is a disk in -- if they always think there is a disk in, then 'write protect' does the right thing when there isn't one. (Sounds to me like, for your mech, you'd need both to nobble the media-change diode, and the 'disk present' switch.) NOTE -- This worked for me. That does not mean I guarantee it will work for you. If you even THINK about opening the case of your mech, on your own hands be it. Good luck. -- Paul Smee, Univ of Bristol Comp Centre, Bristol BS8 1TW, Tel +44 272 303132 Smee@bristol.ac.uk :-) (..!uunet!ukc!gdr.bath.ac.uk!exspes if you MUST)