Obvious access to the MIG is via a 1024-byte (or more... see below) ​window at $CC00 (mirrored at $DE00) that becomes visible only when the aux firmware bank is selected.

+

Access/​control of the MIG is via a $800-byte window ​starting ​at $C800 when the aux firmware bank is selected. ​ The window is repeated at $D800 (I/O select is mediated by the lower half ROM select), but is not usable unless the accelerator is disabled. ​ The lower $600 bytes of this space is shared with the ROM, and the upper $200 bytes is used for the MIG RAM window and other control functions.