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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 8 bits are fixed to 0, and only the lower 24 bits are valid.
Even if a carry or borrow occurs from bit 23 to 24 as a result of branch address calculation, the higher 8 bits
ignore the carry or borrow and remain 0.
Therefore, the lower-limit address of the program space, address 00000000H, and the upper-limit address
00FFFFFFH are contiguous addresses, and the program space is wrapped around at the boundary of these
addresses.
Caution No instruction can be fetched from the 4 KB area of 00FFF000H to 00FFFFFFH because this
area is defined as peripheral I/O area.
instructions in which the destination address will reside in any part of this area.
(2) Data space
The result of operand address calculation that exceeds 32 bits is ignored.
Therefore, the lower-limit address of the program 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.
CHAPTER 3
Figure 3-7. Program Space
Program space
00FFFFFEH
00FFFFFFH
00000000H
00000001H
Program space
Figure 3-8. Data Space
Data space
FFFFFFFEH
FFFFFFFFH
00000000H
00000001H
Data space
User's Manual U13850EJ4V0UM
CPU FUNCTIONS
Therefore, do not execute any branch operation
(+) direction
(+) direction
(–) direction
(– ) direction
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