I'm not sure I can lay hands on the original Apple DOS manual right away, but I
do have a digital simulator that's capable of simulating a PROM, though I've
never used that feature, and perhaps I can whip up a simulation that will
properly illustrate how the prom map and external hardware interact with a data
stream. Presumably if I can get the matter to work on writes, I can then
reverse the process.
Having once done that, I should be able to regenerate the state machine in a PAL
or other device, including, perahaps, some 'C' code to interpret the modulation
into raw data under PC control. A detailed simulation is a pretty good way to
examine the behavior of a circuit, and certainly easier than doing the same
thing with a 'scope and/or logic analyzer.
At the time that WOZ designed this piece of hardware, registered proms were much
less costly than equivalent PALs, and PALs had, associated with them, a
considerable failure rate in testing. Apple did, after all, expect to inspect
their parts as they came in and before they went out.
Dick
----- Original Message -----
From: "Tony Duell" <ard_at_p850ug1.demon.co.uk>
To: <classiccmp_at_classiccmp.org>
Sent: Wednesday, September 05, 2001 3:48 PM
Subject: Re: Apple ][ disk controller state machine
> >
> > Until I get my hands on a copy of the venerable "Beneath Apple Dos"
> > is there anyone who can point me to an online resource describing the
> > Apple ][ disk controller P6 ROM state machine? The exact uses
> > for the Q6 and Q7 switches ($C0EC-$C0EF)? Or would be willing to
> > summarize from the mighty tome for me?
>
>
> I've just pulled out my copy of 'Beneath Apple DOS', and the information
> you need doesn't seem to be in there. There's very little about the disk
> hardware at all -- it assumes you'll at least use the standard routines
> to read/write bytes on the disk.
>
> From the schematics in the Apple DOS manual, it appears that Q7 is
> inverted and turned into the write gate/ line to the disk drive. So
> presumanly Q7 is a write enable input (it does also go to the state
> machine PROM and I guess it sets up the state machine for writing).
>
> Q6 only goes to the state machine, so I have no idea what it's for (I've
> not analysed the state machine -- yet!)
>
> -tony
>
>
Received on Wed Sep 05 2001 - 21:51:49 BST