Writing to Cartridge Port?

Writing to Cartridge Port?

Post by Terry Eva » Tue, 16 Mar 1993 18:51:51

  I'm currently taking some hardware classes at the University
here and we are required to to design some hardware circuts
which need to be simulated.  Well, instead of me having to
flip toggle switches and push a button for the clock to get
my state machines to work, I'd like to write a quick program
to send the necessary pulses to a port.  That way I can just
make some sort of simulation file and send it out and see if
my circut works.  I would like to use the cartridge port because
the parallel and serial ports on my Mega2 ST are already taken.

  So, is there somebody that can give me some info on how to
write to the cartridge port?  You may either post responses

suggestions are also welcome!


Terry Evans


Writing to Cartridge Port?

Post by Brian Gri » Wed, 17 Mar 1993 03:09:04

Writing to the Cartridge port will create a bus error. What has
worked in the past is to define one of the bank selects as a write
strobe and use 8 of the address lines as pseudo-data out lines.
Then by reading an address in the selected bank you are acutally
causing your hardware to write.

Make sure you buffer every line that you are using, or you could
inadvertantly fry your machine, via a glicth from the target system.

Brian (ST/TT User/Developer)
Bell Northern Research
Research Triangle Park, NC


1. writing to cartridge port

  A couple people asked me to post my results on how to write to the
cartrige port.  The easiest method is just using one of the address
bits (the highest or lowest bit are the most logical choices).  So
whenever you do a read from the port space with this bit set, the cartridge
can check this and use the address you passed as the actual data.

There were a couple other methods which require some hacking up of your
computer.  Basically you bring the r/w line out to the cartridge port.
But you also have to cut the lines that cause a bus error whenever you
try writing to the cartridge port (ROM3 and ROM4 if I remember correctly).
On top of cutting these lines you have to add a little hardware to them
so the MMU doesn't get confused.  (I can't remember the exact details now).

Hope this helps...



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