Creating new CP/M disks - Progress on IMSAI

Chuck Guzis cclist at
Sat Jan 12 11:37:06 CST 2008

> 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.



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