Creating new CP-M disks - Progress on IMSAI

Andrew Lynch lynchaj at
Sat Jan 12 17:45:35 CST 2008

-------------Original Message:
Date: Sat, 12 Jan 2008 09:37:06 -0800
From: "Chuck Guzis" <cclist at
<> >
Subject: Re: Creating new CP/M disks - Progress on IMSAI

> Date: Fri, 11 Jan 2008 23:50:27 -0500
> From: "Richard A. Cini" <rcini at
<> >
>     Anyway, one of the issues I have with the Teac FD-55GFR (1.2mb
> high-density; no schematic) drives Im using is that the motor runs all of
> the time (just like an 8 drive) but these late-model Teac drives dont
> have head relays, so the heads are engaged all of the time.

Since the 8272/765 does drive "polling", you have to connect DRIVE 
SELECT/ to DRIVE SELECT/.  Connecting it to MOTOR ON/ would likely 
have some odd effects.  Recall also, that the 765 can do overlapped 
seeks on multiple drives, which requires that the DRIVE SELECT/ line 
be what it says it is.

Which leaves you with connecting HEAD LOAD/ to MOTOR ON/; not a good 
solution if you do a lot of multiple-drive operation (as CP/M floppy 
systems are wont to do).  Better would be to use a timer to monitor 
the HEAD LOAD/ line and keep MOTOR ON/ active for a minute or so 
after the last drive activity.  A (or a couple) of NE555's should do 
the trick.

Recall that with the 55GFR, as the drive will not gate INDEX/ pulses 
until it's determined that the diskette's come up to speed.  (This, 
BTW, is why hard-sector diskettes don't work in a 55GFR).  So if 
you'r getting INDEX/  pulses, the drive, by definition, is ready.

That's not to say that you couldn't get a GFR with a head-load 
solenoid, but they're pretty uncommon.

My take anyway.



That was going to be my last-ditch suggestion for the TEAC, putting a 
one-shot delay on the /MOTOR ON line (Chuck, you know how I love 555s ;-).

That delay on the 55GFR is not only a problem with hard-sector diskettes;
when I went through this exercise replacing 8" drives on my Cromemcos
(soft-sector), the GFR didn't work because the /DS -> /READY delay was 
too long, even with the motor spinning. Tying /READY to ground made it
work and I suppose one could tie /READY to /DS with a diode if one 
had no other drives available.

Interestingly, Andrew Lynch apparently got a different version of the GFR
(-149 IIRC) to work on his Vector with HS disks, whereas my -159 never
goes ready at all with HS disks.

The YE YD-380 does have a HL solenoid but AFAIK it's not separately
controllable; there's a pair of jumpers (HM & HS) that select whether
the head loads on /MOTOR ON or /DS. Nevertheless, it's probably
the closest to an 8" drive with a HL solenoid and constantly running

One thing I've learned from trying to use 1.2Mb HD drives in anything
other than an AT is that among the dozen or so drives I tested there's
almost no consistency at all as far as jumper options and labelling, 
/READY and /INDEX logic, etc. are concerned, even with different 
versions of the same make and model.

One of the most adaptable drive in my limited experience has actually 
been the Panasonic JU-475 FWIW.




Yes, I can attest to what Mike is saying regarding the TEAC FD-55GFR drives.
I have gotten the TEAC FD-55GFR -149's, -193's, and -540's to work reading
16 sector hard sector media on my Vector Graphic with the VEDMCS.  

The frustrating thing is that the TEACs *almost* work perfectly.  There
still is a problem that if the motor turns off, sometimes I get a "BDOS
error, drive not ready" message when accessing the drive.  It seems the
delay to read the drive is just a tad too short.  Oddly enough, the VEDMCS
doesn't even sense /READY pin 34 so it must be computing this value based on
/INDEX or /READ or some other value.  I think tying the /MOTOR line to
ground might fix the problem but then the drives would be constantly
spinning and I don't want that either.

When I use the Panasonic JU-475-1, I don't have the problem.  As a result, I
am probably going to upgrade the Vector to the Panasonic JU-475 style drives
since those are the only ones of several kinds I have tried that operate
trouble free.

Once you leave the AT standard, the HD drives vary a *lot* and there is no
telling what will work short of just experimenting and testing.  There are
variations within brands and models, the jumpers have wildly varying
meanings, if they are even there at all.


Andrew Lynch

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