NEC PD703114, Руководство пользователя

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CHAPTER 3 CPU FUNCTION
59
User’s Manual U15195EJ5V0UD
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 branch address calculation, the higher
6 bits ignore the carry or borrow.
Therefore, the upper-limit address of the program space, address 03FFFFFFH, and the lower-limit address
00000000H 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. No instruction can be fetched from this area because this area is defined as
on-chip peripheral I/O area. Therefore, do not execute any branch address calculation in
which the result will reside in any part of this area.
03FFFFFEH
03FFFFFFH
00000000H
00000001H
Program space
Program space
(+) direction ( ) direction
(2) Data space
The result of an operand address calculation that exceeds 32 bits is ignored.
Therefore, the upper-limit address of the program space, address FFFFFFFFH, and the lower-limit address
00000000H are contiguous addresses, and the data space is wrapped around at the boundary of these
addresses.
FFFFFFFEH
FFFFFFFFH
00000000H
00000001H
Data space
Data space
(+) direction ( ) direction