Wrap-Around Of Cpu Address Space - NEC V850E/MA1 User 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. Even if a carry or borrow occurs from bit 25 to 26 as a result of a branch address calculation, the
higher 6 bits ignore the carry or borrow.
Therefore, the lower-limit address of the program space, address 00000000H, and the upper-limit address
03FFFFFFH become contiguous addresses. Wrap-around refers to a situation like this whereby the lower-
limit address and upper-limit address become contiguous.
Caution The 4 KB area of 03FFF000H to 03FFFFFFH can be seen as an image of 0FFFF000H to
0FFFFFFFH. This area is access-prohibited. Therefore, do not execute any branch address
calculation in which the result will reside in any part of this area.
03FFFFFEH
03FFFFFFH
00000000H
00000001H
(2) Data space
The result of an 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 FUNCTION
Program space
(+) direction
Program space
Data space
(+) direction
Data space
User's Manual U14359EJ4V0UM
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