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Chapter 3
CPU Function
User’s Manual U16702EE3V2UD00
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 a 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.
Figure 3-14:
Program Space
(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.
Figure 3-15:
Data Space
03FF FFFEH
03FF FFFFH
0000 0000H
0000 0001H
Program space
Program space
(+) direction
(–) direction
FFFF FFFEH
FFFF FFFFH
0000 0000H
0000 0001H
Data space
Data space
(+) direction
(–) direction
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