uhclem@trsvax.UUCP (11/18/88)
The following information is provided by an individual and is not nor should
be construed as being provided by Radio Shack or Tandy Cory. Radio Shack/
Tandy Corp has no obligation to support the information provided in any way.
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NOTE:
The following information was posted about a month ago. However, I posted
a draft version and not the version I intended to, and only noticed this
after receiving some inquires about it. The following information supercedes
the posting with the date 28-Aug-88. Sorry for the error.
P.S. Note: Sent this out but somewhere in the virus crisis it seems to have
not gone anywhere. To those that are seeing it again, Sorry. Just press J.
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6000 > 4000 > 3000 Vol 1, No. 1
Utilizing 5 1/4" media on your Tandy 16/6000 computer system. 31-Aug-88
by Frank Durda IV
If you have reached the point where you are having trouble getting 8"
media, or getting the drives repaired or replaced, this 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 $34.95. If you buy your disks at those prices, it will
take 20 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 $20,
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.
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 you have 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 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 external 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, 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: Not all the 5 1/4" disk drives will 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.
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If you have questions about this article, please send email to:
Frank Durda IV @ <trsvax!uhclem>
...decvax!microsoft!trsvax!uhclem
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