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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 set to "0", and only the lower 24 bits are valid.
Even if a carry or borrow occurs from bit 23 to bit 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. The above-mentioned state in which the lower-limit and the upper-
limit addresses of the memory space are contiguous addresses is called wraparound.
Caution
No instruction can be fetched from the 4-Kbyte area of 00FFF000H to 00FFFFFFH because
this area is defined as 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.
00FFFFFEH
00FFFFFFH
00000000H
00000001H
(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.
FFFFFFFEH
FFFFFFFFH
00000000H
00000001H
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CHAPTER 3 CPU FUNCTIONS
Program space
(+) direction
Program space
Data space
(+) direction
Data space
User's Manual U11969EJ3V0UM00
(–) direction
(–) direction
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