Partial Success report...
I've now got a cart board (made of a dead Pitfall cart) that I can plug a 27256
into, with any game burned to the first 4k of the EPROM, and it will actually
play on a 2600... What I actually did was to solder a 24-pin socket into the
24 pins on the cart board, then plug a 28-pin socket into that, with selected
pins bent out so they don't make contact (the 27256, like most (all?) other
EPROMs, has an active low chip enable, and also has a separate active low
output enable. The /OE pin is where A11 would normally go...)
The thing looks awful, it's a patchwork of jumper wires and hot glue, I think
I'll call it FrankenCart...
The next steps (not necessarily in this order):
- Fix my colortwk.bin so it works on a real Atari (works fine in PCAE and z26...)
- Wire DIP switches with pull-up resistors to the top 3 address lines, so I can
use the rest of the EPROM.
- Play lots of River Raid!!!
- Build a bank-switched version for 8k rom images.
- Get back to work on my crappy game, make it non-crappy...
For the bank-switched version... I don't know the standard way to do this, but
I have a few 13-input AND gate ICs, and lots of invertors, so I should be able
to wire all the address lines to the inputs of the AND gate (and the unused
input to Vcc), and invert the appropriate ones, until I have a gate that will
trigger when the magic memory location is accessed. Then I need a what, a
flip-flop or something, to control the A12 line of the chip?
My roommate and I built this thing together, he's in the other room trying to
build another one, with DIP switches, right now... So I should go help.
Adieu,
Brian
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