CHAPTER 3 CPU FUNCTIONS
3.4.3 Wraparound of CPU address space
(1) Program space
Of the 32 bits of the program counter (PC), the higher 6 bits are fixed to 0 and only the lower 26 bits are valid.
Even if a carry or borrow occurs from bit 25 to bit 26 as a result of branch address calculation, the higher 6 bits
ignore this and remain 0.
Therefore, the lower-limit address of the program space, 00000000H, and the upper-limit address,
03FFFFFFH, are contiguous addresses, and the program space is wrapped around at the boundary of these
addresses.
Caution No instructions can be fetched from the 4 KB area of 03FFF000H to 03FFFFFFH because this
area is an on-chip peripheral I/O area. Therefore, do not execute any branch operation
instructions in which the destination address will reside in any part of this area.
Program space
03FFFFFEH
03FFFFFFH
(+) direction
(–) direction
00000000H
00000001H
Program space
(2) Data space
The result of an operand address calculation that exceeds 32 bits is ignored.
Therefore, the lower-limit address of the data space, address 00000000H, and the upper-limit address,
FFFFFFFFH, are contiguous addresses, and the data space is wrapped around at the boundary of these
addresses.
Data space
FFFFFFFEH
FFFFFFFFH
(+) direction
(–) direction
00000000H
00000001H
Data space
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