Advice for Tek 4051 vector-drawing issue?

[Christian Corti]

On Sun, 22 Feb 2009, Josh Dersch wrote:
> Richard wrote:
>> I guess the best way to get data transferred from these systems is to
>> use the GPIB interface and transfer the programs out of the system and
>> into the internet.  I wonder if the easiest would be to use a
>> Commodore GPIB compatable floppy drive or something.
>> 
> Or over the optional RS-232 expansion (at a whopping 2400bps).  I've been 
> experimenting with this idea for archiving 405x tapes (and Bob Rosenbloom has 
> offered to lend me a couple of tapes to play with) but the major catch is 
> that the 4051 appears to _only_ be programmable in BASIC -- there's no 
> PEEK/POKE or ways to call user 6800 machine code.  This wouldn't be a problem 
> except that it's possible to protect tape files with the "SECRET" command -- 
> this makes a given file execute-only, so it appears to be impossible to read 
> the contents of the file using BASIC commands.  I'm guessing that most (if 
> not all) commercial software tapes are protected in such a manner, but I 
> suppose I'll find out.

We have several third-party ROM and RAM modules for our 4051. A RAM module 
(called BACKRAM) behaves like a ROM module after you have loaded the 
contents from tape. There is one module with support for CBM drives, 
special I/O routines, assembler and firmware routines.
The documentation (alas German only) for these ROMs can be found at 
ftp.informatik.uni-stuttgart.de/pub/cm/tek4051/

BTW it *is* possible to write 6800 programs, it's just not officially 
documented. The magic command is
CALL "exec" [,{Var1} [,{Var2} {,...]]], {Loaderstring}
(see exec.txt and ram_loader.prg)

> I'm looking into whether if it's possible to adapt one of the "backpack" 
> expansions to take EPROMs instead of MCM6832 ROMs.  Anyone done this before? 
> Given a bit of hacking it'd then be possible to write some 6800 code to do a 
> binary dump of the tapes, bypassing the protection mechanisms.

I've already written a little BASIC program that uses the special ROM 
functions in order to create real tape dumps into a CBM floppy file. These 
dumps contain all records etc., and it is possible to create a real tape 
from that image. The commands are TREAD and TWRITE.

The file sysrom.txt contains a descriptions of the system ROM entry points 
and the function they perform.

And here's how to un-secret a program (see exec.txt):

L$="7?008039"
CALL "exec",L$


Christian