rpw3@amdcad.AMD.COM (Rob Warnock) (07/07/87)
Hardware alert: The following is for people who change lightbulbs, and
other hardware jobs, not for "pure" programmers... ;-} ;-}
Despite good intentions and all sorts of available communications programs,
by July 2nd I still hadn't gotten Minix up on my Toshiba T1100+ yet, mainly
due to its not having 5-1/4" disks (it uses 720K 3-1/2" hard-shell floppies,
like the Mac). You see, the external 5-1/4" floppy option on that beast is
over $400 (around here), and given the impending total embargo on Toshiba
products (see your local newspaper) I'm collecting my bucks to buy the
"expansion chassis" option (lets you plug in PC cards).
Still, though I had offers to put stuff on 3-1/2" disks (thanks, Bdale!),
I knew that I really needed a 5-1/4" drive for communications with others
around here who have PCs, so I decided to graft on my own external floppy.
(Should be simple, no?)
Unfortunately, Toshiba doesn't document the pinouts on the 25-pin connector
on the back, the one that's shared between the external floppy (can be either
disk "A" or "B") and the parallel printer. So I engaged in a little electrical
sleuthing, and figured it out the hard way (with the help of a voltmeter and
many LEDs and an oscilloscope). I believe I've succeeded [Minix boots!], and
present the results herein. May it be of some use to someone else.
DISCLAIMER: There are no guarantees that this information is correct,
reliable, or safe. While I am indeed using the connection described in
my own system, I cannot guarantee that it will function in yours, or
that it will not damage your system. There are at least two ambiguous
pairs of signals in the pinouts [which I think don't matter, see below],
and other pins which I show as "unused", even though they appear to have
termination voltages on them. [Anyone having better information as to
the "official" pinouts, please correct me.]
If you are not enough of a hardware hacker to scrounge the appropriate
connectors and jumper cables, you probably shouldn't try this. However,
some hints may help:
I used a half-height Mitsubishi drive ($80 at Fry's, for Bay Area folk), and
for the external power supply used one of the ones Radio Shack has these days
for $5 that are surplus from ColecoVision (seem to work, but I'm a bit worried
that 300ma of +12v might not be enough), and a "power-strip" as a power switch
(the R/S supply is a "wart-on-the-wall", and has no switch).
You need a convenient way to scramble-wire the 25-pin DB-25 on the back
of the T1100+ to the 34-pin PC edge-connector on the floppy. My solution
was to make up a small 25-pin straight-through extension cable, buy a
standard 34-pin floppy cable (the other end has the usual .1"-grid push-on
header), and mount a pair on connectors on a piece of perf-board to do the
scramble-wiring. (As it turned out, if the floppy is right next to the T1100+,
I can leave out the DB-25 extension, and plug the perf-board "adapter" directly
into the back of the T1100+.) Total cost: ~$100 (plus a few hours of my time,
which I don't count because I was having fun!)
Enough verbiage, the goodies:
T1100+ DB-25 pin Signal name Floppy edge-connector pin
---------------- ----------- -------------------------
01 Ready 34 [Note#1]
02 Index 08 [Note#1]
03 Track0 26
04 Write-Protect 28
05 Read-Data 30
06-09 (n/u) [Note#3]
10 Select 10 [Note#2]
11 Motor-On 16 [Note#2]
12 Write-Data 22
13 Write-Enable 24
14 (n/u) [Note#3]
15 Head-Select 32
16 Step-Direction 18
17 Step-Pulse 20
18-25 GROUND All odd pins (1-33)
Notes:
#1. It appears that Ready and Index are AND'ed together inside the T1100+
controller, since the disk worked equally well whichever signal was
connected to pins 01 or 02. The assignment given above was chosen
arbitrarily.
#2. It appears that Select and Motor-On are are driven by the same signal
inside the T1100+ controller, since the disk worked equally well whichever
signal was connected to pins 10 or 16, and I did not see any difference
on a 'scope. The assignment given above was chosen arbitrarily.
#3. Pins 6-9 and 14 seem "unused", though they do have +5 "pullups" on them.
(This may be due to those signals being used when the port is selected
as the parallel printer.)
#4. All signals are "active-low", and are pulled up to +5 by the T1100+ when
inactive.
As I said above, it seems to work fine: MS-DOS "format" works, MS-DOS floppies
can be read and written, and Minix boots and reads /usr.
"On to the enthralling job of overhauling... Minix?" (Apologies to G. B. Shaw)
Rob Warnock
Systems Architecture Consultant
UUCP: {amdcad,fortune,sun,attmail}!redwood!rpw3
ATTmail: !rpw3
DDD: (415)572-2607
USPS: 627 26th Ave, San Mateo, CA 94403bdale@winfree.UUCP (Bdale Garbee) (07/13/87)
In article <17392@amdcad.AMD.COM> rpw3@amdcad.UUCP (Rob Warnock) writes: >Unfortunately, Toshiba doesn't document the pinouts on the 25-pin connector >on the back, the one that's shared between the external floppy (can be either >disk "A" or "B") and the parallel printer. So I engaged in a little electrical >sleuthing, and figured it out the hard way Wrong. It just isn't in the manuals that come with the box. Would you give a software jock connector pinouts? That's *DANGEROUS*! Toshiba does run a customer support BBS at 1-714-837-4408, 1200 baud only. I got the number by calling the 800 voice number and asking a techie-type question. There is a file on the board called 3100-ibm.txt, which docs the cable in question, along with files that doc all the other connectors. Sorry you went to so much trouble before you asked! Here's the file, I haven't bothered to check your work Rob: 1100+ or 3100 to IBM Floppy Disk Male DB-25 to 34 pin Card Edge connector 1 33 & 34 2 8 3 26 4 28 5 30 6 to 9 nc 10 12 11 16 12 22 13 24 14 nc 15 32 16 18 17 20 18 to 25 All odd pins >You need a convenient way to scramble-wire the 25-pin DB-25 on the back >of the T1100+ to the 34-pin PC edge-connector on the floppy. I just crimped ribbon cable into an edge connector, flared the other end, and soldered the individual wires to the tabs of a solder-cup style DB25. Works great with a shell around the DB25 for strain relief. Has been in use for months... (how did you think I got Minix on the Toshiba in the first place!!) -- Bdale Garbee, N3EUA phone: 303/593-9828 h, 303/590-2868 w uucp: {bellcore,crash,hp-lsd,hpcsma,ncc,pitt,usafa,vixie}!winfree!bdale fido: sysop of 128/19 packet: n3eua @ k0hoa, Colorado Springs