* slot 1 to Upper 0 / Upper &81 (BASIC)
* slot 3 to Upper 7 / Upper &83 (AMSDOS)
* all other slots to &80 + number
That's basic Plus cartridge behaviour. It doesn't fully decode RMR2 to set other exotic mappings as the Play2CPC does. That's only required for it to serve as full external replacement for the internal Plus cartridge port, but as far as I (Abalore) know no software uses it but maybe the Burning Rubber + BASIC cartridge.