The FSTAT register is at RegisterBase + 0x105. Since it is possible to relocate the register table on the S12, we have to specify each register in the form (BaseAddress + Offset).
On the S12, the INITRG register is used to specify the BaseAddress for the RegisterTable. As is happens, the default base address is 0x0000, and so unless you make any changes, you should see FSTAT at 0x0105.
Mark