Nf-ID: #R:xvt.com:9918:nemesis:-30996:000:11641
Nf-From: nemesis.UUCP!uhclem    Nov 18 21:09:00 1992


[0]I'm looking for information on how to modify a 16B/6000 for 5-1/4" drives.
[0]I understand that such a mod has been devised and may even have been posted
[0]on the net previously. (I've been patiently waiting for it to get reposted.)

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                     6000 > 4000 > 3000      Vol 1, No. 1
        Utilizing 5 1/4" media on your Tandy 16/6000 computer system.
     by Frank Durda IV  Copyright 1988, 1990, 1991.  All Rights Reserved.
              Original Version 31-Aug-88 - Last Updated 1-Jun-91
       Originally published on USENET in comp.sys.tandy, September 1988

       This article may be  republished in  part  or  in  its  entirety
       provided  credit  is  given  and  the material is made available
       without charge.

       A modest media charge is acceptable IF  the  recipient  has  the
       option  of  providing  their own media to duplicate the material
       onto at no charge.  Any other use of this  material   must  have
       prior written approval.

       Commercial bulletin boards and other information  servers  (like
       Compuserve(R))  who  place  an  additional  copyright or similar
       restriction on material that is retrieved from their system  MAY
       NOT  distribute  or  archive  this  article.   UUNET and freely-
       accessible ftp/uucp sites are allowed to archive/distribute this
       article.

If you have reached the point where  you  are  having  trouble  getting  8"
media,  or  are  faced  with the prospect of getting the drives repaired or
replaced, this article may interest you.

The following information will allow you to add or substitute 5  1/4"  high
capacity  floppy  drives  for  8" double sided drives in your 16/6000 XENIX
system.  You can mix 8" and 5 1/4" drives, or chuck the 8" drives entirely.

If you just want to look at the pay-back, pull out your handy  Radio  Shack
computer  catalog.  Ten 8" DD DS disks cost $39.95.  Ten 5 1/4" HD DS disks
cost $18.95.   If you buy your disks at those prices, it will take  just  5
boxes  of  5  1/4" vs 8" diskettes to pay off the approx $100 drive.  Since
most mail order houses can get you ten 5 1/4" HD DS for less than $10, a  5
1/4"  drive  will  pay  back a lot quicker.  In addition, most people would
agree that 5 1/4" media  quality  is  usually  better  than  the  8"  media
available today.

If you want to add 5 1/4" drives externally, you should obtain an enclosure
to  mount  the  drives  in.   These  are available from numerous mail-order
houses.  One is AEROCOMP, 2544 West Commerce St, Dallas Tx 75212, P.O.  Box
223957  and  the order number is 1-800-527-0347.  (Sorry, I have never done
business with this firm, so  I  can't  comment  on  their  product.)   They
advertise an enclosure for two 5 1/4" drives.  You could also order such an
enclosure from Radio Shack National Parts (it was used for CoCo  drives  in
recent years).

Almost any high-capacity (1.2 Meg) drive can be used.   I  used  Mitsubishi
MF504B-347UA  drives.   For  that  particular drive, these straps should be
set:
        TD MS SR-PM2 RI SB DSx
Other drives that should be acceptable include TEAC 55G series drives.

Warning:  If the drive only has DSx straps,  it probably cannot be used.
          This type of drive is pre-configured to be used with an IBM-AT
          disk  controller   and  will  not  work  with  anything  else.

DSx should be set as you prefer.  On a Model 16B and 6000 drive 0  may  not
be  selected on the external connector.  If you have two internal drives on
a 16B/6000 and want to keep using them, your external drives  must  be  DS2
and DS3.  The last external drive must contain a terminating resistor pack.

If you only have one internal drive, you may have  three  5  1/4"  external
drives.  Set the strap DS1 for the first drive, DS2 for the second, and DS3
for the third.

If your 16B/6000 has two internal 8" drives and you wish to disable one  of
them,  it  will  be  necessary to disassemble your 16B/6000, and disconnect
power and data  cables  going  to  your  second  internal  drive.   If  the
terminating  resistor pack is installed on the drive you are disconnecting,
you must move the resistor pack to drive 0.  By  disconnecting  the  power,
you  will  reduce  the power consumption and heat load on your system.  You
must also add a jumper at E40-E41 on the 16B/6000 main CPU board (under the
card cage).  This moves the DS1 signal to the external connector.

If you have a Model II or 16A, you can have at least  two  external  drives
and  as  many  as  four  if  you  decide  to  disable  the internal drives.
Initially it is suggested that you leave drive 0 as an 8" drive  until  you
can copy your installation floppies onto 5 1/4" media.

On the Model 16A, 16B and 6000, it is advised that you leave  one  internal
drive  connected to power even if you decide to disconnect its data cables.
This is to insure a minimum load on certain power supply voltages.

You must construct the cable between the Model II/16A/16B/6000  and  the  5
1/4"  drives.  You will need a 50 pin dip connector and at least one 34 pin
edge connector  (one per drive).  You may use either 34 or 50 pin wire.

If you have an existing 50 pin cable and a 34 pin  cable,  you  may  simply
wish  to  cut  the connector off one end and splice the appropriate signals
together.  Just try to keep the total length to under 6'.

Because the cable you build may be delicate, you may want to build it as  a
short  cable which can fit entirely inside your drive enclosure with the 50
pin connector mounted so that a longer  standard  50-to-50  pin  cable  can
connect  between  the computer and the drive enclosure by plugging into the
"translation" cable.

Here is the wiring table.  Keep in mind that the odd numbers are ground  on
both the 34 and 50 pin connectors.  The new cable should re-route the wires
in pairs to help simplify assembly and assure  adequate  ground.   When  an
entire group of wires can be moved as a set, they are listed together.

Signal Name             50 Pin  tie to  34 Pin
                       connector       connector
                        Pins            Pins

Side Select (14)        14-15           31-32

Index (20)              20-21           7-8

Ready (22)              22-23           33-34

Drive Select 1 (26)     26-31           9-14
Drive Select 2 (28)
Drive Select 3 (30)

Drive Select 4 (32)     32-33           5-6

Direction (34)          34-47           17-30
Step (36)
Write Data (38)
Write Gate (40)
Track 0 (42)
Write Protect (44)
Read Data (46)

Again, note that on both connectors the odd numbered pins  are  ground  and
even  numbered  pins  are  the  signals.   Do not get the ground and signal
reversed. For example,  the  Index  signal  line,  pin  20  on  the  50-pin
connector,  connects  to  pin 8 on the 34-pin connector.  21 connects to 7.
When dealing with a group of signals such as  "26-31  goes  to  9-14",  you
would  have  26->10, 27->9, 28->12, 29->11, 30->14, 31->13.  By putting the
edge or DIP (but not both ends) connectors  "on  the  wrong  side"  of  the
ribbon  cable, the cabling system itself will assist in getting the correct
alternations.

In addition to the above, pins 9 and 10 on the 50  pin  connector  must  be
tied   together  to  produce  the  "double-sided"  signal  that  the  Model
16/16B/6000 requires.  All other pins on the 34 and 50 pin connector should
not be connected to anything.  Your cable can look like this:

        +---+                           +-----+        +-----+
        ! 5 !--------\           /------!  3  !--------!  3  !
        ! 0 !--------\ A miracle/-------!  4  !--------!  4  !
        !   !-N/C       occurs----------!     !--------!     !
        ! p !------------here-----------!  p  !--------!  p  !
        ! i !--------/          \-------!  i  !--------!  i  !
        ! n !-------/               N/C-!  n  !--------!  n  !
        +---+                           +-----+        +-----+
        DIP                              Edge           Edge
    (facing down)                     (facing up)     (facing up)

That is all there is to it.  Once you have built your  cable,  and  applied
power  to your drive enclosure, connect the cable to your Model 16/16B/6000
external floppy connector (on the 16B/6000 it is behind the access door and
in  the  lower  right corner), and turn on your system.  If the drive light
comes on and stays on, this usually indicates that the cable is plugged  in
upside down somewhere (check your pin 1 keying).

If the drive light does not light, run diskutil and  attempt  to  format  a
floppy in that drive.  If the drive light does not come on, check the drive
select strap on the drive and make sure it is set to the drive  number  you
tried to format.  If that is ok, the cable may be at fault.

If the drive light does come on but diskutil does not get past cylinder  0,
the  terminating  resistor may not be installed or the cable is incorrectly
wired.

If diskutil gets all the way through formatting a floppy, and it behaves as
though it formatted a double sided disk, you are in business.

If you have some programs that are hard coded to expect  media  in  certain
drives   under   XENIX,  consider  renaming  the  device  names  (/dev/fdn,
/dev/rfdn, /dev/fdbtn and /dev/rfdbtn) so that you can  use  5  1/4"  media
instead.   Be sure to rename all the floppy devs with the same drive number
or else you can get into trouble.

Although the 5 1/4" drives are 80 track drives, only 77 of the  tracks  are
used  under 6000 XENIX, because it still thinks it is talking to a 77-track
8" drive.  However, because 6000 XENIX writes the correct number of sectors
per  track  allowed  for  that  transfer  rate and motor speed (16 512-byte
sectors), the XENIX-usable storage will equal 1.224 meg (((76x2x16)+16)x512
=  1,253,376, which is 24K more than the IBM AT format allows.  The full 80
tracks can be utilized,  but  this  requires  patching  and  more  operator
intervention when performing tars dumps and file-system creation.  This and
passing data between IBM AT and a 6000 XENIX system on 5 1/4" disks will be
discussed in a future issue.

One final note:  5 1/4" disk drives will not detect a  diskette  change  as
the  earlier  8"  half-height  drives  did  (most had square lights).  (The
cost-reduced 8" drives usually had round drive lights and these would  only
report  a disk change if it occurred while the drive light was on.) Because
there is no separate signal line available, some 5 1/4"  drives  simply  do
not  provide that information while others combine it with the READY signal
or some other signal.  On the drives I used, I found that attempting to use
the  combined  READY  and DISK CHANGE caused numerous problems so the above
straps do not enable that feature.  If  you  obtain  a  different  type  of
drive,  you  need  to strap it so that the READY signal indicates READY and
nothing else.

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If you have questions about this article, please send email to:

                                Frank Durda IV @ <m6000@nemesis.lonestar.org>
                                ...utacfd!nemesis!m6000   (Internet route)
                                ...rwsys!nemesis!m6000
                                ...decvax!microsoft!trsvax!nemesis!m6000
                                or from CompuServe:
                                >INTERNET:m6000@nemesis.lonestar.org