8.10.2 Extended I/O Registers
The I/O memory space ranging from 0x0040 to 0x103F can only be accessed by the
LD/LDS/LDD
or ST/STS/STD
instructions,
transferring data between the 32 general purpose working registers (R0-R31) and the I/O
memory space.
Refer to Table 9-1 and the Instruction Set Summary section for further details.