Wrap-Around Of Cpu Address Space - NEC V850ES/SA2 UPD703201 Manual

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.
0 3 F F F F F E H
0 3 F F F F F F H
0 0 0 0 0 0 0 0 H
0 0 0 0 0 0 0 1 H
(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.
F F F F F F F E H
F F F F F F F F H
0 0 0 0 0 0 0 0 H
0 0 0 0 0 0 0 1 H
72
CHAPTER 3 CPU FUNCTION
Program space
(+) direction
Program space
Data space
(+) direction
Data space
Preliminary User's Manual U15905EJ1V0UD
(−) direction
(−) direction