Path: utzoo!utgpu!watserv1!watmath!att!att!linac!uwm.edu!cs.utexas.edu!usc!ucsd!ucbvax!PUCC.PRINCETON.EDU!MQUINN%UTCVM
From: MQUINN%UTCVM@PUCC.PRINCETON.EDU
Newsgroups: comp.sys.apple2
Subject: Re: Disk // register listing
Message-ID: <9011030453.AA02428@apple.com>
Date: 3 Nov 90 04:08:43 GMT
References: <cs4w+@ANDREW.CMU.EDU>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 109

On Fri, 2 Nov 90 17:12:29 GMT Charles William Swiger said:
>Anybody have a detailed description of the $C0Ex range of addresses?
>(Which are the registers that control a 5.25" drive at the lowest level
>possible.)
>
>I've disassembled DOS 3.3 RWTS, the $C600 boot code, parts of ProDOS,
>etc and the function of some locations are obvious, but others aren't.
>Thanks.
>
>
>
>-- Charles William Swiger
>    cs4w+@andrew.cmu.edu

ADDRESS    LABEL     DESCRIPTION
-----------------------------------------------------------------
$C080     PHASEOFF    Stepper motor phase 0 off.
$C081     PHASEON     STEPPER MOTOR PHASE 0 ON.
$C082     PHASE1OFF   STEPPER MOTOR PHASE 1 OFF.
$C083     PHASE1ON    STEPPER MOTOR PHASE 1 ON.
$C084     PHASE2OFF     {                 }
$C085     PHASE2ON      { YOU CAN FIGURE  }
$C086     PHASE3OFF     {   OUT THESE     }
$C087     PHASE3ON      {                 }
$C088     MOTOROFF    TURN OFF MOTOR.
$C089     MOTORON     TURN MOTOR ON.
$C08A     DRVOEN      ENGAGE DRIVE 1
$C08B     DRV1EN      ENGANE DRIVE 2
$C08C     Q6L         STROBE DATA LATCH FOR I/O
$C08D     Q6H         LOAD DATA LATCH.
$C08E     Q7L         PREPARE LATCH FOR INPUT.
$C08F     Q7H         PREPARE LATCH FOR OUTPUT.

       Q7L WITH Q6L = READ
       Q7L W/ Q6H = SENSE WRITE PROTECT
       Q7H W/ Q6L = WRITE
       Q7H W/ Q6H = LOAD WRITE LATCH

---------------------------

You need to at $x0 to $C08n where x is the slot number.

---------------------------

Addresses $C080 through $C087 are for moving the drive arm.  The arm moves in
QUARTER tracks so each access to one 'SET' of those addresses moves the arm
1/4 a track:

LDA $C0E0
LDA $C0E1

will move the arm a quarter track ($C0E0 for slot 6).
To move a whole track, cycle through the whole set of stepper motor phases:

LDA $C0E1
LDA $C0E0
LDA $C0E3
LDA $C0E2
.
.
LDA $C0E7
LDA $C0E6

The first access to one of these addressess starts up the arm and the other
stops it.  To move the arm in the opposite direction, cycle through these
the other way (the PHASEON of each set always comes first).

You must start the drive up before (or turn it on) by accessing $C0E9 first.
Immediately after starting it up, you must tell it WHICH drive:

LDA $C0EA ---->  access drive 1
LDA $C0EB ---->  access drive 2

You might want to set it to READ first, immediately after starting up the
drive.  I can't remember how to do this, you could probably figure it out
with the Q6L - Q7H things and a scratch disk.
You can also check to see if the disk is write protected with those four
addresses, although I can't recall how right now.
The data latch out $C0EF is the address you write to to actually write a
byte to disk, but you must have enabled write mode first somehow using
Q6 and Q7 H&L.  To READ from the disk, read from address $C0EE, but you
must first anable reading AND allow the drive time to get up to speed.

For those of you wondering why ProDOS anly allows two drives per slot, it's
probably because there are only two addresses per slot ($C0xA & $C0xB) to
determine which drive to access.

I got this info from "Beneath Apple DOS"... The most useful book I've ever
read to this date.  I imagine that "Beneath Apple ProDOS" would be even
better.  Anyone got a copy they want to sell?
By the way, those books are from Quality Software

If there is anyone that hasn't read either of these books, I HIGHLY recommend
them!  "Beneath Apple DOS" covers virtually every conceivable thing you would
want to know about DOS 3.3, including copy protection schemes and how to
break them and even how to make your own (It's easier to make your own than
to crack one :)
Even though these books are outdated (well, the ProDOS one may not be), they're
still EXTREMELY informative on Disk Operating Systems in General.  I find mysel
f explaining how DOS's work to sceniors in computer science and even to
computer science proffessors just from the stuff I learned from the DOS 3.3
book!

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