Re: Pinout for Disk II and IIc/IIc plus disk ports

[dempson@actrix.gen.nz (David Empson)]

Frank Townsend <ftownsen@iamdigex.net> wrote:

> While looking for a DB19 M/F cable, I found the following which sounds like
> what you're looking for.
> 
> http://ground.ecn.uiowa.edu/apple2/MiscInfo/IIc/prout
> 
> It's apparently all from the Apple TIL:
> 
> External Floppy Drive Connector
> -------------------------------
> 
> The Apple IIc external disk drive port is a DB-19 connector. The signals
> available at the port are as follows:
> 
> 10 - WRPROT
> 1 - GND
> 11 - SEEKPH0
> 2 - GND
> 12 - SEEKPH1
> 3 - GND
> 13 - SEEKPH2
> 4 - GND
> 14 - SEEKPH3
> 5 - +12V
> 15 - /WRREQ
> 6 - + 5V
> 16 - NC
> 7 - +12V
> 17 - /DR2
> 8 - +12V
> 18 - RDDATA
> 9 - /EXTINT
> 19 - WRDATA

Whoa!  Pin 5 is -12V, not +12V.

Pin 17 is normally drive 1 enable.  This happens to enable drive 2 for
the IIc, since it already has an internal 5.25" drive.  This signal is
actually the enable line for the first connected 5.25" drive.

Note that /EXTINT (pin 9) is unique to the Apple IIc.  For all other
implementations of this connector, pin 2 is drive 2 enable.  The first
UniDisk 5.25 or Apple 5.25 Drive will redirect this signal to pin 17 of
its daisy-chain connector, so that both drives use pin 17 to select
them.

(Everything works differently for a 3.5" drive, with different rules for
the Apple 3.5 Drive and SmartPort devices like the UniDisk 3.5.)

Here is a full list of the signals for the three types of 5.25" drive,
courtesy of Open-Apple volume 1 number 11.

Signal                         Uni-DuoDisk  IIc external   Disk ][

GND       Ground Reference         1-4           1-4       1,3,5,7
-12       -12 volts DC              5             5           9
+5        +5 volts DC              6,16           6         11,12
+12       +12 volts DC             7-8           7-8     13,15,17,19
WRPROT    write protect            10            10          20
PH0-3     stepper motor phases    11-14         11-14      2,4,6,8
WRREQ     write request            15            15          10
ENBL      drive enable            17,(9)         17          14
RDDATA    read data                18            18          16
WRDATA    write data               19            19          18
EXTINT    external interrupt       n/a            9          n/a
          not connected            n/a           16          n/a

The Disk ][ controller has separate connectors for each drive, and the
two connectors have identical signals, except for pin 14, which comes
from the appropriate drive enable line.

If you want to build an adaptor from the IDC-20 used with the Disk ][ to
the D-19 used on later drives, it is _almost_ a straight ribbon cable
connection, using a ribbon cable mounting D-19.  The exceptions are:

D-19 pin 9 should go to pin 14 for drive 2 (it would normally go to pin
17 on the IDC-20 if you use a direct ribbon cable connection).

D-19 pin 10 should go to pin 20 on the IDC-20 (it would normally go to
pin 19 on the IDC-20).

IDC-20 pins 17 and 19 should not be connected.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P O Box 27-103, Wellington, New Zealand