
CHAPTER 3 CPU FUNCTION
User’s Manual U15905EJ2V1UD
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3.4.3
Wrap-around of CPU address space
(1) Program space
Of the 32 bits of the PC (program counter), the higher 6 bits are fixed to 0 and only the lower 26 bits are valid.
The higher 6 bits ignore a carry or borrow from bit 25 to 26 during branch address calculation.
Therefore, the lowest address of the program space, 00000000H, and the highest address, 03FFFFFFH, are
contiguous addresses. That the lowest address and the highest address of the program space are contiguous
in this way is called wrap-around.
Caution
Because the 4 KB area of addresses 03FFF000H to 03FFFFFFH is an internal peripheral I/O
area, instructions cannot be fetched from this area. Therefore, do not execute an operation in
which the result of a branch address calculation affects this area.
Program space
(+) direction
(
) direction
03FFFFFEH
03FFFFFFH
00000000H
00000001H
(2) Data space
The result of an operand address calculation operation that exceeds 32 bits is ignored.
Therefore, the lowest address of the data space, 00000000H, and the highest address, FFFFFFFFH, are
contiguous, and wrap-around occurs at the boundary of these addresses.
Data space
(+) direction
(
) direction
FFFFFFFEH
FFFFFFFFH
00000000H
00000001H