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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 6 bits are set 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 calcula-
tion, 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 the situation that the
lower-limit address and upper-limit address become contiguous like this.
03FFFFFEH
03FFFFFFH
00000000H
00000001H
Caution: No instruction can be fetched from the 4 KB area of 03FFF000H to 03FFFFFFH
because this area is defined as peripheral I/O area. Therefore, do not execute any
branch address calculation in which the result will reside in any part of this area.
(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 Function
Figure 3-7: Wrap-around of Program Space
Program space
Program space
Figure 3-8: Wrap-around of Data Space
Data space
Data space
Preliminary User's Manual U14913EE1V0UM00
(+) direction
( ) direction
(+) direction
( ) direction
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