Torsten,
Your right, there isn't much documentation about the 7800 cartridges. About
the best info I found was on Dan Boris web site. He has some descriptions
of the type of boards used in some 7800 cartridges he has taken apart. This
would give you at least on idea of which cartridge (if you have extras of)
to rip apart and use.
The basic premise behind 7800 bankswitching evolves around the use of a
74LS373 or 74LS374 depending on the type of cartridge it is found on (Super
Cart 1 or Super Cart II or Supercart III). J.A. Valdez was the Atari
engineer whose name I saw associated with a lot of the 7800 cartridge
designs.
The 373 or 374 is used as a high address line switcher. Data lines D0 - D2
are used to select one of 8 possible banks. A bank can be selected by
writing a value between 0 and 7 to any address in the range of $8000 -
$BFFF. Bankswitching on the 7800 is described in the 7800 Developers
manual.
Bank 0 thru 6 reside in the $8000 - $BFFF region of 7800 memory. These
banks correspond to the various 16k chunks in an EPROM. For example a
27C010 EPROM can hold 128K bytes of information. It can also be looked at
as eight 16K byte banked ROMs. So banks 0 thru 6 will be these 16K byte
banked parts of a 27C010.
Bank 7 is mapped to $C000 - $FFFF region of memory. And is also the last
16K byte chunk of a 27C010 (if the game goes on a 1Meg ROM).
You can also have extra static RAM on the 7800 cartridge or extra ROM. This
RAM or ROM is mapped to the $4000 - $7FFF region. The RAM is either a 6264
(8k byte) or a 62256 (32k byte) static RAM chip. 16k chips were never
developed, that's why a 32k is used (in fact the 7800 developer board does a
neat trick by using that extra 16k to store the debugging code). And the
ROM chip is typically a 27128 EPROM.
One big problem with the 7800 game boards that use 1Meg of ROM space is that
they were designed for Mask programmable chips only. Meaning that the chip
is program when the chip die is made (hard coded into the chip). The chip
is only 28 pins in size. All EPROMs of that size are 32 pins. So you have
to do some creative soldering to make it fit. Fortunately, the majority of
the pins are in relative same position if you align the chips from their
bottom ends (pins 14/16 and 15/17 end; opposite end of the notch).
Besides the Supercarts on the 7800 there is the 32k and 48k carts. The 48k
cart is just a modified 32k cart. So depending on the size of the game and
it's memory requirements, there are lots of choices on the 7800. There a
web site out there that also has a hardware hack for the 7800 to allow you
to dump carts onto a PC and convert a basic 7800 cartridge into a 32k byte
storage device to do hobbyist level programming on it.
I believe the XEGS Super Carts do some of the same basic switching except
that it's confined to the cartridge port memory in the Atari 8bit. It uses
a 74LS374 type of chip and the Cartridge Control Line, CCTL signal, to do
the switching with. Switches out a 16K bank at a time. The XE Demo Cart is
neat in it's ability to switch between games by doing a power cycle on the
computer. Uses a capacitor as a power source to keep the memory circuit
alive long enough to remember what game it was on before power was turned
off.
Well, I hope I gave you enough information to move on with your project.
Good luck. I'll email you a chart that I have on a 7800 cart jumper
settings that I have in a Word document.
Regards,
Glenn Bruner
glenn.bru@verizon.net
"Torsten Schall" <inf@worms.fh-rpl.de> wrote in message
...
> Hi 7800/XLE nerds,
> i've two little problems (they are nearly the same)!
> Problem one 7800:
> I wanted to burn some of the prototypes i found in the internet but
couldn't
> find any docs about the bankswitching cartrides (7800) and the used rom
types.
> I could modify a Xevious 32KB cart to run the internet version of
Xevious and
> Pete Rose Baseball, everything (X/PRB) burned on a 27256.
> Now i am trying to burn some 128KB games on rom and use a different cart
> Scrapyard Dog/Karateka.
> How are the banks switched?
> I also wanted to read out my original roms, what is the pinout of the roms
that
> Atari used in the 7800.
> Problem two XLE:
> I need the Pinout/Chip type for the Atari XLE Supercartridges.
> I am !!!!trying!!!! to modify some games.
> I have the 1MBit Rom Emulator with the the doku/info from John
Skruch/Atari.
> They used 27128 eproms for the banks.
> This info is on the homepage of Jindrush
> look XEGS carts.
> I am very happy about every info that helps me to go on.
> Thanks, happy Atari 8 Bitting
> PS: I looked at many 7800 homepages but the don't described the functions
of the
> jumpers nor the pinout of the used roms.
> --
> Mit freundlichen Gruessen
> Torsten Schall
> E-Mail: Torsten.Sch@fh-worms.de