Date   : Sat, 25 May 1991 06:46:20 GMT
From   : agate!spool.mu.edu!mips!swrinde!cs.utexas.edu!helios!tamuts!jdb8042@ucbvax.Berkeley.EDU (John Donald Baker)
Subject: 5.25" on 8" controller

I have recently begun the process of putting 5.25 80-track (high-density) disk
drives on by 8" disk controller.  Although I have had some initial success,
I have hit a few snags that some people on this newsgroup may be able to help
me solve.

For the record, the significant parts of my system are:
     Extended-keyboard Apple //e (PCPI Applicard for CP/M)
        SVA ZVX4 Dual-Density 8" disk controller (in Slot 7)
           2 Shugart SA801 Single-Sided Disk drives (SA800 mode, Soft sector)

The 5.25"drives I'm adding are TEAC FD55GFR's (2).  The drives have been
jumpered for their appropriate addresses (DS2, DS3) and position 34 on the
card edge supplies a READY signal.  All corresponding interface signals have
been mapped from the 8" controller 50-pin connector to the 5.25" drives'
34-pin connector with the exception that HEADLOAD is applied to the IN-USE
position and IN-USE is applied to MOTOR-ON.

At this time, the drived are strapped to turn the motor on when the front
bezel light is lit.  This causes the drives to begin running when they are
selected, but since the controller does not de-select a drive after initial
access, they continue to run until another drive is selected.
Currently, this works to advantage because a second access is necessary to
permit a disk operation to succeed. This is most likely because either the
5.25" drive does not come READY fast enough for the controller to acknow-
ledge or the controller expects the drive to be ready before issuing 
HEADLOAD or IN-USE signals.

Question 1:  How may I get the disk drives to start up only when actually
            accessed (not just selected) and stop when done.
Question 2:  What solution(s) are there to the apparent time-out on the
            drive (not ready in time)?  The soolution to this may also
            provide a solution for Ques. 1.

Qestion 3:  What are symptoms of a drive system with too many terminators
           installed?  Can this condition manifest itself in the form of
           errors while formatting disks?  (The 5.25" drives' terminating
           resistiors are soldered in and the drives are in parallel with
           the 8" drives [rather than chained after them] which also have
           otherwise proper termination [drives DS0, DS1 with terminators
           on DS1] for only two drives.  I have been able to format disks
           with the 5.25" drives, but there are considerable errors in the
           process with the drive designated DS2 at the end of the 5.25"
           chain [tee].

Pleas note that any and all solutions must be compatible with 8" drives
remaining in the system.

I remember seeing a description of a small circuit which solved the problem
of DRIVE READY timeouts, perhaps the person who wrote that message could
email it to me as per my .sig.

Thanks for the help.

John D. Baker  ->An Apple 3.5", 5.25", 8" PCPI Applicard ZCPR3 nut//
Internet:  JDB8042@{tamuts|rigel|sigma|summa|zeus|venus|ceres}.tamu.edu
BBSs:  JOHN BAKER on Z-Node #45 [(713) 937-8886], The Vector Board
[(716) 544-1863], The Phoenix: [(713) 495-3039], The Black Box (FIDO
1:106/601) [(713) 480-2686], O.U.C.H. FOG-20 [(713) 777-2114]
Karnache: "Fire at will!"
Wil (desperately dodging a hail of automatic weapons fire): "AAAAIYEEEE!!"
Karnache: "No, no.  Do not fire at Wil, he is my Second Mate.
           FIRE AT THE SEA-DUCK!!"