Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!ccu.umanitoba.ca!herald.usask.ca!alberta!ubc-cs!van-bc!zaphod.mps.ohio-state.edu!sdd.hp.com!spool.mu.edu!uunet!munnari.oz.au!uhccux!uhheph.phys.hawaii.edu!ralph From: ralph@uhheph.phys.hawaii.edu (Ralph Becker-Szendy) Newsgroups: comp.os.cpm Subject: re: Using 3.5" floppies instead of 8" floppies Summary: Pin listing and some caveats Message-ID: <11375@uhccux.uhcc.Hawaii.Edu> Date: 9 Feb 91 07:16:06 GMT Sender: news@uhccux.uhcc.Hawaii.Edu Organization: U of Hawaii High Energy Physics Lines: 104 Since someone asked what the method is to hook up a 3.5" floppy disk drive instead of an 8" drive, here is a listing of pin-numbers on the cables. A 5.25" HD or 3.5" HD floppy is electrically nearly equivalent to a 8" DD floppy. The only major difference is that some 5.25" HD and all 3.5" HD floppy drives spin at 300RPM (instead of 360RPM, what it used to be for 8" floppies), so you can pack more data onto each track (but you don't have to). Some 5.25" HD drives switch to 360 RPM when switching to HD mode though (usually jumper selectable). All odd pins on both cables are ground. 8" floppies use a 50-pin cable, 3.5" and 5/25" floppies use a 34-pin cable: Pin Pin Signal 50p 34p ================== 12 4 Disk change (may be on other pins too, not very standarized) 14 32 Side select (some 8" drives use no side select, instead two different drive select lines) 18 2 Head load (all 5.25 and 3.5" drives ignore this, sometimes use the pin for something else) 20 8 Index pulse 22 34 Ready (some 5.25 and 3.5" drives have no ready) 26 10 Drive select 0 28 12 Drive select 1 30 14 Drive select 2 (not all 5.25 and 3.5" drives have that) 32 6 Drive select 3 (not all 5.25 and 3.5" drives have that) 34 18 Step direction 36 20 Step pulse 38 22 Write data 40 24 Write gate 42 26 Track zero 44 28 Write protected 46 30 Read data 16 Motor on (only some 5.25 and 3.5" drives) Going from this list to a special-wired cable should be easy. Supposedly there are some 3.5" floppies which also get their +5V supply fed through the data cable. Never seen one yet (at least never taken one apart). To emulate a 8" drive you have to set up the 5.25" or 3.5" drive to work in HD mode. Some 3.5" drives can sense the density-indicator hole in the floppy, others need a DENSITY SELECT signal from the controller, sometimes on pin 2, sometimes on pin 34. If the controller doesn't supply that, one can emergencies just use ground or Vcc instead and leave them permanently in HD more. Sometimes one can find the multiplexer on the controller which switches between 5.25" SD/DD mode (250kHz data rate) and 8"/HD more (500kHz data rate), and use the signal which controls that multiplexer to switch the drives between normal and high density. If the 5.25" or 3.5" drive really needs the MOTOR ON signal (most newer ones can be jumpered to do the motor control themselves), just strap it to ground, that keeps the engines under full steam. If your controller needs a READY signal from the drive and the drive does not generate one, take the SELECT signal you use to select the drive, delay it by a few hundred ms with a 74121 and use that for READY. Some controllers even work with a connection between READY and SELECT (or even more cruel, just grounding READY so the drive is always ready); you might get read errors when selecting the drive for the first time (while the floppy spins up to speed), but one or two retries will cure that; most controllers / BIOSes will retry automatically. Problem: The controller (and thereby your BIOS) can not determine whether there is a floppy in the drive. On the real 8" drives and on 5.25" drives I get a "NOT READY" error immediately when I try to use a drive with no diskette in it; on the 3.5" drive it takes about 30 seconds, while the controller re-tries like mad, and finally I get a "RECORD NOT FOUND" error from my BIOS. Annoying but survivable. For the real meaning of the DISK CHANGE, READY, MOTOR ON and DENSITY SELECT lines you have to consult the manual for the drive. I have access to manuals for a few drives (Toshiba, Sony, Shugart, Panasonic), mail me if you need help with those. Most drives can have all these critical pins changed via jumpers. On some 5.25" HD drives there are about 30 or 40 jumpers, so setting up the drive can turn into a real science, and can probably not be accomplished by trial and error any more. Some 8" disk drives can have very elaborate selection schemes (binary select, where SELECT 0 is a global select and SELECT 1-3 are a 3-bit drive address), or they use weird combinations of select lines instead of SIDE SELECT to switch between the two sides. If one really >has< to emulate such madness, a few TTL gates might be required. One more weirdness: 3.5" drives usually have non-removable terminators in the kOhm range, instead of the good old ~200 Ohm removable terminators. I have never tried using just a 3.5" drive at the end of a long flat cable with no other termination, and it probably is a real bad idea since reflections must be fierce. I never understood why people would want to replace 8" drives. They are friendly, solid, reliable, and teach respect for computers. I have lost a 3.5" disk drive in the pile of stuffs on my desk; that could never happen to an 8" drive. Installing a 2-drive set with power supply is very good exercise and builds character and muscles. They heat the office, and provide a pleasant acoustic background (I call mine the "afterburner"). You will never forget a 8" floppy in your shirt pocket and run it through the washer by mistake. In emergencies, you can remove the floppy from the jacket, and for a limited time read and write on a naked floppy. If you screw up aligning the heads really bad, a little pile of brown dust will form under the drive and you hear a screaching noise; on 3.5" disk drives you can't even align the heads yourself. On the other hand, they don't have that cute sliding shutter which one can play with. Well, guess I can't have everything. -- Ralph Becker-Szendy UHHEPG=24742::RALPH (HEPNet,SPAN) University of Hawaii RALPH@UHHEPG.PHYS.HAWAII.EDU High Energy Physics Group RALPH@UHHEPG.BITNET Watanabe Hall #203, 2505 Correa Road, Honolulu, HI 96822 (808)956-2931