From what I can find the card has a 3 byte address register which auto increments when a data register is accessed for either reading or writing. The addresses of the registers depends on the slot the card is plugged into but is in the $C000-$C033 area.
Some of code uses absolute indexed X addressing with a base address in the $BFF8-BFFB range so that any dummy reads generated by LDA/STA abs,X will not affect the registers.
I'm not sure this is exactly the same as the official Apple card.
https://github.com/a2retrosystems/mxp/tree/master/slinky/diagshttps://github.com/a2retrosystems/mxp/tree/master/slinky/romThis schematic is for a 256K card with the same kind of interface
http://john.ccac.rwth-aachen.de:8000/patrick/data/256k_RAM.pdf