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From: david@uow.edu.au (David Wilson)
Newsgroups: comp.sys.apple2
Subject: Re: db-19 drive cable compatibility: A2 vs Mac
Date: 6 May 98 02:51:43 GMT
Organization: University of Wollongong, NSW, Australia.
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buggie@musca.unm.edu (stephen e buggie) writes:

>      COMPATIBILITY EXPERIMENTS OF APPLE II VS. EARLY MAC
>                    DB-19 DISK DRIVE CABLES

>	I am unable to get the Mac db-19 cables to run with Disk II.  Last
>weekend, I tediously measured PINOUTS on the A2 db-19 cable vs. the older
>Mac db-19 cables.  Here are the disturbing results:

>	First, the A2 db-19 cable uses 18 lines, while the Mac db-19 cable
>uses only 17 lines.  For A2, pins 5 and 9 are used, and pin 16 is vacant.
>The Mac db-19 cable is vacant on pin #5.

>	Is there any hope of modifying the Mac db-19 cable to make it work
>with A2?  How vital is pin #9 wire line in the A2 drive cable?  I have
>toyed with the idea that I could run a jumper in the A2 male plug from
>pin 5 to pin 16, then on the IDE-20 change the crimp pin to position 5.
>But this would do nothing about pin #9 ...


Here are the pinouts from Nathan's web page:

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        -         -

As you can plainly see, pin 5 supplies the -12V used by the Disk ][ drive.
No pin 5 => no -12V => no function. Have a look at the circuit diagram of
the Disk ][ (in the DOS manual) to see what the -12V is used for.

Pin 9 is the second drive select and is not needed unless you intend to
daisy chain drives.
--
David Wilson  School of IT & CS, Uni of Wollongong, Australia  david@uow.edu.au