Date   : Wed, 14 Feb 1990 06:03:39 GMT
From   : titanic.cs.wisc.edu!tonyrich@speedy.wisc.edu (Anthony Rich)
Subject: MOVCPM's "copy protection"

Good news/Bad news:

Thank you to David Goodenough for showing me how to work around the
"synchronization error" message.  The good news is that his tip allowed
me to run MOVCPM; the bad news is that it didn't do any good, since
the resulting CP/M image hangs.  A previous posting to this newsgroup said
that the serial-number comparison isn't really copy protection, it's
to make sure you get a valid resulting image.  Apparently that's correct.

The upshot is that I have to have my copy of MICAH CP/M running in order
to reconfigure it so I can get it running.  (That's a tough one!)

FYI, I WAS using a program called DEBUG...it's Cromemco's version of DDT.
(Since I didn't have a reliable CP/M to boot with, I had to boot with
Cromemco CDOS to do my fiddling with my CP/M boot disk, see.  CDOS isn't
completely CP/M compatible; it can read CP/M 8" disks, but lots of CP/M
programs crash under CDOS, which is why I bought MICAH CP/M in the first
place.)

If anyone still cares, here's the workaround that David sent me:

> There are two copies of the serial # in the BDOS/CCP image: mine were at
> 1200H and (about) 0D20H in the MOVCPM.COM program (when loaded). Here's
> how to find them:
> 
> The CCP copy comes right after the command table, so hunt for the
> 'DIR ERA USER' strings, they're all glued together, part way up the
> CCP, and the serial # comes right after them (the next 6 bytes).
> 
> The BDOS copy is just at the start of BDOS, so look for the '$$$     SUB'
> fcb towards the top - it's followed by a bunch of zeroes and then on the
> next page boundary, you'll find the serial # again.
> 
> At about 02CBH in the MOVCPM.COM program is the code that tests it: I found
> 
>     LD    HL,(????)
>     LD    DE,1200        ; address of the BDOS serial # in the core image
>     ...
>     LD    C,6
> 
> then some ld, cp etc. stuff, and a
> 
>     JP    NZ,SOMEWHERE
> 
> If you nuke the JP NZ, it ought to work.   [It does.  -T.R.]
>
> dg@lakart.UUCP - David Goodenough
--
Email:       tonyrich@titanic.cs.wisc.edu  Phone:  608-271-8450
Disclaimer:  The opinions above are mine.  Others may agree or disagree.


End of INFO-CPM Digest V90 Issue #25
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