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From: dempson@atlantis.actrix.gen.nz (David Empson)
Subject: Disk ][/UniDisk 5.25 Adaptor Cable
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Date: Thu, 11 Jan 1996 14:34:01 GMT
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Making a Disk ][/UniDisk 5.25 Adaptor Cable
by David Empson (dempson@actrix.gen.nz)
Disclaimer: This article describes a moderately complicated procedure for
making up a cable to connect a disk drive to a different type
of controller. I am assuming the reader is reasonably
proficient with the necessary tools and terminology. This is
not a straightforward procedure, and if the cable has any
mistakes, you run the risk of damaging your computer, disk
controller and/or disk drive.
I will not accept any responsibility for any such damage - you
make this cable entirely at your own risk.
Here are the details of how to make an adaptor cable to allow a UniDisk 5.25
(or equivalent, such as the DuoDisk, Apple 5.25 Drive or Disk //c) to be
connected to a Disk ][ controller card, or to connect a Disk ][ to a UniDisk
5.25 controller, or IIgs or IIc disk port.
Much of this information comes from page 90 of Open-Apple Volume 1, number 11
(1985).
The following table lists all of the drive control signals for each type of
controller card/disk port.
signal function Unidisk IIc IIgs Disk ][
GND ground reference 1-4 1-4 1-3 1,3,5,7
-12V -12 volts DC 5 5 5 9
+5V +5 volts DC 6,16 6 6 11,12
+12V +12 volts DC 7,8 7,8 7,8 13,15,17,19
WRPROT write protect 10 10 10 20
PH 0-3 stepper motor phases 11-14 11-14 11-14 2,4,6,8
WREQ write request 15 15 15 10
DRVEN drive enable 17 (9) 17 17 (9) 14
RDDATA read data 18 18 18 16
WRDATA write data 19 19 19 18
EXTINT external interrupt - 9 - -
3.5DISK Apple 3.5 drive enable - - 4 -
HDSEL 3.5" drive head select - - 16 -
not connected - 16 - -
The UniDisk uses pin 9 to select the second drive. Inside each UniDisk,
the signal from pin 9 at the computer is connected to pin 17 of the daisy-
chain drive connector. When the computer selects drive 2 by activating
pin 9, the first drive passes this through and the second drive sees its
enable signal on pin 17. Thus all drives are identical.
The Disk ][ controller has two drive connectors, and the same pin (14) is
used on each connector to select the appropriate drive. This signal is
the only difference between the connectors - all other signals are
connected in parallel.
Despite the IIgs having special functions for pins 4 and 16, they may be
ignored when dealing with 5.25" drives, and treated as a UniDisk controller
(i.e. connect pin 4 to ground, and pin 16 to +5V). The Apple 3.5 drive
disconnects these signals internally, so that they will not interfere with
its operation.
The UniDisk, IIc external drive and equivalents use a DB-19 connector, in
which the pins are numbered along the connector, i.e.
1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19
The Disk ][ uses an IDC-20 (20 pin insulation displacement connector) in
which the pins are numbered in columns, i.e.
2 4 6 8 10 12 14 16 18 20
1 3 5 7 9 11 13 15 17 19
The above numbering is from the back of the plug (where the ribbon cable
connects to the plug). If you are looking at the front of the plug (the
socket side), reverse the rows in the above diagram (top row is 1, 3, ...)
With a ribbon-cable mounted IDC-20, pin 1 of the cable (the one with the
red stripe) goes to pin 1 of the connector, pin 2 of the cable goes to
pin 2 of the connector, etc. To be on the safe side, I always use a
continuity tester to confirm the position of pin 1 by testing it with
cable wire 1.
The pin numbering of the DB-19 connector does NOT correspond to the wire
numbers in the cable. Pin 1 of the cable goes to pin 1 of the connector,
but pin 2 of the cable goes to pin 11 of the connector.
The above table indicates the pinouts of the drive controllers. The
corresponding drives have identical pinouts, except that the IIc external
drive does not use the "EXTINT" signal (it has never been used by any
device, as far as I know).
Due to the zig-zag mapping of the pin numbers on the DB-19, there is an
almost 1:1 correspondence of signals between the Disk ][ and UniDisk
connectors. The following table shows the wire numbers used by the
UniDisk, with the Disk ][ for comparison.
signal function Unidisk Disk ][
WIRE NUMBERS
NOT PIN NUMBERS
GND ground reference 1,3,5,7 1,3,5,7
-12V -12 volts DC 9 9
+5V +5 volts DC 11,12 11,12
+12V +12 volts DC 13,15 13,15,17,19
WRPROT write protect 19 20
PH 0-3 stepper motor phases 2,4,6,8 2,4,6,8
WRREQ write request 10 10
DRVEN drive enable (low) 14 (17) 14
RDDATA read data 16 16
WRDATA write data 18 18
The only differences are wires 17, 19 and 20 (using the Disk ][ numbering).
Now that we have the necessary background information, here are the details
for the various types of cables that can be made up.
Connecting a UniDisk (or equivalent) to a Disk ][ controller
============================================================
There are five possible sub-cases here.
(a) A Disk ][ controller with a single UniDisk connected as drive 1.
(b) A Disk ][ controller with a Disk ][ as drive 1 and a UniDisk as drive 2.
(c) A Disk ][ controller with a UniDisk as drive 1 and a Disk ][ as drive 2.
(d) A Disk ][ controller with two UniDisks, connected with separate cables.
(e) A Disk ][ controller with two UniDisks, connected in a daisy-chain.
All of cases (a) through (d) require the same cable. In each case, a
UniDisk is being adapted to a 20-pin connector that was intended for a
Disk ][ drive.
Case (e) requires a cable which has signals going to both drive connectors
on the Disk ][ card. I will describe this cable, then the differences
between it and the first cable.
Required parts:
- One female IDC-20 ribbon cable header;
- One female ribbon cable mounted DB-19;
- A short length of 20-way ribbon cable (I recommend three inches),
with a red stripe at pin 1 (or with each wire coloured differently);
- A vise (or some other method of clamping the connectors to the cable);
- A sharp knife with a fine point, e.g scalpel or skill knife;
- A pair of wire cutters and strippers;
- A soldering iron and solder;
- A short length of heatshrink or insulation tape;
- A continuity tester ("beeper").
1. Note the position of pin 1 of the connector on the Disk ][ controller.
With the card facing you and the slot connector down, it is the pin on
the left at the front of the connector.
2. Identify pin 1 of the IDC-20 connector. With the socket side facing
down and the IDC-20 held horizontally, it is the pin in the front left
corner. The cable must come out of the IDC-20 on the same side as pin
1, since it plugs into the Disk ][ card with no room at the back.
If the IDC-20 has a locating notch, it must be facing outward, i.e. on
the same side as pin 1.
3. Clamp the IDC-20 to one end of the cable, making sure the cable is
oriented correctly and that the red stripe goes to pin 1. If you
are using a multi-colour ribbon cable, note which colour is pin 1.
4. Poke a short piece of wire into pin 1 of the IDC-20 and verify that it
is connected to pin 1 of the cable. Repeat this in turn for each
pin, also checking for shorts against adjacent wires in the cable.
5. Separate pin 20 from the cable at the free end. Use the wire cutters to
cut the insulation between pins 19 and 20, then peel pin 20 back by about
an inch. This is needed because the DB-19 only has 19 cable contacts.
Do not cut into the wire for pins 19 and 20 - we will need them later.
6. Get the DB-19 connector, and note the pin numbering (the pins should be
labelled on the socket side, at the very least). Clamp the DB-19 to
the free end of the cable, ensuring that pin 1 of the DB-19 goes to
cable pin 1. There are two possible orientations of the connector (on
the top or bottom of the cable). Either works equally well, so take
your pick.
7. Use a pair of wires poked into each hole of each connector to verify the
connection. There should be no shorts between adjacent pins (note that
the adjacent pins at the DB-19 end zig-zag between the rows).
8. Now we need to modify the cable. Near the IDC-20 end, cut wire numbers
17 and 19 about half an inch from the connector. Do not cut wire 18.
Also cut wire 20, but leave about an inch on the IDC-20 end. Peel off
the remaining off-hang of wire 20 (if any) and put it aside. Separate
the overlap on wires 19 and 20, and use the wire strippers to remove a
little insulation from the cut end of each wire (the end going to the
DB-19 for wire 19, the end going to the IDC-20 for wire 20).
9. If you are using heatshrink, put it onto one of the wires now, back from
the end (separate one of the wires from the cable as far as needed).
10.Solder the stripped ends of wires 19 and 20. You should end up with a
wire running from pin 10 of the DB-19 to pin 20 of the IDC-20. Cover the
soldered junction with heat-shrink (use a heat gun to tighten it) or with
insulation tape.
If you are making a cable to connect a single UniDisk to a Disk ][ card (i.e.
cases (a) to (d) above, the following steps are not required.
11.Peel back wire 17 on the DB-19 side, and strip off a little insulation.
Do the same with the off-cut wire from pin 20 (that was put aside
earlier). Solder the ends together, and use heatshrink or insulation
tape to cover the join. This wire needs to go to the second drive
connector on the Disk ][ card (pin 14). If you don't mind modifying the
card semi-permanently, you can solder the wire onto the card. Look at
the back of the Disk ][ controller, around the area of the connector for
drive 1. Above pins 12 and 14 is a feed-through (the only one above the
connector). This carries the select signal for drive 2. The wire can
be soldered at this point. Alternatively, solder it onto pin 14 on the
back of the card, on the drive 2 connector.
If you want a less permanent modification, use a second IDC-20 and solder
the wire onto pin 14 of the connector, then plug this into the drive 2
position. Another option would be to use a single square molex pin,
pushed onto pin 14 of the drive 2 connector on the card.
12.Finally, test the cable again, using the first table in this article.
Pins 1 to 8 and 11 to 18 of the DB-19 should be unaffected, and go to
pins 1 to 16 of the IDC-20. DB-19 pin 9 should go to the loose wire
which goes to pin 14 of the drive 2 connector. DB-19 pin 19 should go
to IDC-20 pin 18. DB-19 pin 10 should go to IDC-20 pin 20. IDC-20
pins 17 and 19 should not be connected to anything.
See the end of this article for a picture of the completed cable.
Finally, test the cable by plugging the drive 1 and 2 connectors into the
card. I suggest powering up the computer without any drives connected,
just to make sure that nothing goes bang. If all seems well, power off
again and connect one UniDisk 5.25. Verify its operation. If all seems
well, power off again and connect a second UniDisk 5.25 in daisy-chain
fashion. Verify its operation.
Connecting a Disk ][ to a UniDisk controller (or IIc/IIgs disk port)
====================================================================
A Disk ][ may be connected to the end of a SmartPort/UniDisk daisy-chain.
The possible ports are:
UniDisk 5.25 controller: maximum of two 5.25" drives (any type).
Apple IIc disk port: maximum of one external 5.25" drive (any type).
Apple IIc+ disk port: maximum of two 5.25" drives (any type).
Apple IIgs disk port: maximum of two 5.25" drives (any type).
Universal Disk Controller: maximum of two 5.52" drives (one per connector,
I think - I've never used a UDC).
When connecting 5.25" drives to a disk port that also supports 3.5" drives
(IIc, IIc+, IIgs or UDC), the 5.25" drives must be connected last in the
daisy chain.
There are two possible adaptors that can be made up.
(a) Connect a single Disk ][ drive at the end of the daisy chain.
(b) Connect two Disk ][ drives at the end of the daisy chain (two
drive connectors).
Cable (a) is dead easy: it is identical to the cable used to connect a
single UniDisk to a Disk ][ controller card (described in the previous
section, as far as step 10), except that the sex of the connectors is
reversed: use a male cable mounted IDC-20 and a male cable mounted DB-19.
Cable (b) is left as an exercise for the reader. The easiest way to make
it is probably to do the same as cable (a) with two male IDC-20 plugs
clamped onto the cable (with the earlier modifications before the first
connector), and re-routing wire 17 to wire 14 beyond the first connector.
A Diagram of the Completed Cable
================================
The original version of this file has a BinSCII-encoded ShrinkIt
archive, which has an Apple Preferred Format (IIgs) picture showing the
pinout of the adapator described in the first section. I drew this
using HyperCard IIgs (with help from some scripts to get everything to
line up properly). The picture is taken directly from the previously
mentioned article in Open-Apple.
If anyone wants a copy of this file, E-Mail me. If I get enough
requests, I'll post the picture of the cable to comp.binaries.apple2.
--
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand