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Re: Zip Chip programming info / disk image?

Jorge Chamorro Bieling wrote:

Linards Ticmanis <ticmanis@gmx.de> wrote:



Jorge Chamorro Bieling wrote:



No... usually the loop runs forever, until data is there.
Is that what happens when you power it up without disk ? (keeps waiting there forever) 

Yes and no. It waits for D5 AA 96 to appear. If it doesn't, it'll just
run on and on and on. But...



But, if you boot and then remove the disk you'll get i/o errors..?
So somehow it quits instead of entering an endless loop.
...if the drive motor is running but there is no disk in the drive, you'll read back random data. It's unlikely that the random data will 
ever match D5 AA 96 unless you keep it running almost forever. But the
random data is enough to terminate the simple LDA ... BPL... loop that's
normally used to wait for a single byte.



I see... although it is an endless loop it won't lock because sooner or
later the msb is going to be set, by the data in a disk or by noise if
there's not a disk in the drive.

Then, I guess, if it was not because of the head stepper, a zipchip (or
anyother accelerator) at full speed could probably use a Disk II for
*reading* without any (timing) problems... right ?


There are some other places in RWTS that depend on timing, such as the
"disk is up to speed" determination.  It might work, but there might
be some I/O errors, too.

It's pretty much moot, since you have to slow down for stepper motion,
and that means you have to detect references to the /DEVSEL space and
slow down, which gets everything else by default.

-michael

Music synthesis for 8-bit Apple II's!
Home page:  http://members.aol.com/MJMahon/

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