My code is now on a chip that was made in 2017! Great, now how do I get it to talk to a machine that was designed in the mid-70's?

After numerous attempts at trying to cram the EEPROM into the cartridge slot, I've gone for the meticulous route of designing a custom circuit and reproducing it using proto-board and cannibalized Atari cartridges.

Not wanting to go through the trouble of having to design and pay for a custom pcb, I used an old Combat cartridge pcb to handle the "plugging in to the Atari part", a zif socket to hold the EEPROM and a bunch of wires from an old LPT printer cable.

Here's what I was thinking electrical wise:

The cartridge port acts as a pretty straight-forward bus for the Atari's Data lines (pink dots in the schematic) and Address lines (green dots). Pin 6 on the top row acts as the chip select, which had to be inverted since the Atari's original mask roms have the CS line active high rather than low like in the EEPROM. All other address lines on the EEPROM are pulled low.

And when I finally went to assemble everything according to the schematic, I goofed.

The Combat rom was only 2k.

SYNDRUM is 4k.

There was no A11 address line (and subsequently, no A11 pin) on the Combat cartridge. Instead of panicking and instinctively hurling a half-finished circuit board at the nearest brick wall, I instead super-glued a bit of metal where an A11 address line should have been and soldered it to it's respective bit of wire.

The result is something that's definitely not pretty to look at and works only if you have your tongue at the right angle, but it DOES work!