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Chapter 3
CPU Function
Preliminary User’s Manual U15839EE1V0UM00
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
calculation, the higher 6 bits ignore the carry or borrow.
Therefore, the lower-limit address of the program space, address 0000 0000H, and the upper-limit
address 03FF FFFFH become contiguous addresses. Wrap-around refers to the situation that the
lower-limit address and upper-limit address become contiguous like this.
Figure 3-7:
Wrap-around of Program Space
Caution:
No instruction can be fetched from the 4 KB area of 03FF F000H to 03FF FFFFH
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 0000 0000H, and the upper-limit
address FFFF FFFFH are contiguous addresses, and the data space is wrapped around at the
boundary of these addresses.
Figure 3-8:
Wrap-around of 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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