NEO-ZMC
Z80 memory controller. Has a hardwired 32KiB bank and switchable 16/8/4/2KiB banks arranged as a register file. To save pins the high address lines (A15-A8) are used for data input. The chip's write strobe is (port) address decoded inside the console.
(Need Z80 IN instructions details: upper 8 bytes of address bus as data, lower 8 as port number)