Date   : Wed, 10 Jun 1987 12:33:47 EDT
From   : <SAGE@LL.ARPA>
Subject: ZCPR on Tandy Model 4

Reply to Rob Healey -- posted to the net for general interest
 
                                                June 9, 1987
 
   I do not personally know of anyone running ZCPR on the Tandy 4, but that
does not mean it has not been done.  Is my recollection right that the Tandy
versions of CP/M are peculiar in that they use a base address of 4000H
instead of 100H?  If that is the case, it is much trickier to get the code
right.  I can try to leave a message on Z-Node Central and see if any user
responds.  Unfortunately, I will be leaving shortly on a month's trip, so I
may not be around to receive the answer.
 
   I would expect ZCPR1 to work on just about any system with a Z80
processor, since it is a direct code replacement.  No other changes to the
system are required.  ZCPR3 is another story completely.  The BIOS has to be
moved down to make room for the buffer modules, and the coldboot code has to
be modified to initialize them.  If Montezuma CP/M makes it DIFFICULT to
drop in a new command processor, it probably makes it IMPOSSIBLE to change
the BIOS.
 
 
                                                June 10, 1987
 
   We had our Boston Computer Society meeting last night, and one of the
area Tandy experts was in attendance.  From what he told me, Montezuma CP/M
is a standard implementation that runs programs at 100H.  It was the earlier
Tandy machines that had the peculiar loading address I described above.
 
   In the ZCPR33 Users Guide I describe a technique for installing ZCPR33
without using SYSGEN but using a disk utility program instead.  The
technique in the exact form I described there won't work in your case, but
it can be adapted.  The basic idea is to create a file with an image of the
operating system component you want to install (for example, ZCPR.COM,
ZCPR33.COM, or ZRDOS.BIN).  You then go in with a late-model disk utility
program that supports a queue.  You go to the file containing the image and
suck it up into the queue.  Then you go to the sector on the system track
where that operating system component is stored and flush the queue out on
top of it.  You should be able to use that technique to get ZCPR1 running on
your system.  The only time it will fail, I think, is when the system tracks
and data tracks on the disk use a different format (that is the case on my
BigBoard I with double-density upgrade -- the first system track is always
single density).
 
   Getting ZCPR3 running still requires moving the system down to make room
for the buffers.  Unfortunately, the person I got my information from could
not remember whether there was a full MOVCPM program included with the
Montezuma CP/M.  One's hopes are often falsely raised by seeing MOVCPM.COM
on the disk.  The manufacturer is supposed to install a relocatable version
of HIS BIOS into that utility, but many manufacturers ship the utility as it
comes from Digital Research -- with the Intel MDS-800 BIOS in it!!!!  If you
are lucky and have a real MOVCPM, you should be able to get Z3 working
without inordinate effort.  The change to the coldboot code can be handled
by patching.  If you get that far, I would be glad to provide further
instructions at that time.  Also, even if the BIOS cannot be moved, things
are not hopeless.  There are tricks that can overcome even that, but they
are even more elaborate (I had to do that with my Wave-Mate Bullet -- they
provided neither MOVCPM nor BIOS source).  Again, if you are up to it, I
would be happy to provide more detailed information.
 
-- Jay