Recommended Use Of Address Space - NEC V850E/RS1 User Manual

3.4.6 Recommended use of address space

The architecture of the V850E/RS1 requires that a register that serves as a pointer be secured for
address generation when operand data in the data space is accessed. The address stored in this
pointer ±32 KB can be directly accessed by an instruction for operand data. Because the number of
general-purpose registers that can be used as a pointer is limited, however, by keeping the perform-
ance from dropping during address calculation when a pointer value is changed, as many general-pur-
pose registers as possible can be secured for variables, and the program size can be reduced.
(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. Regarding the program space, therefore, a 64 MB space of contiguous addresses
starting from 00000000H unconditionally corresponds to the memory map.
To use the internal RAM area as the program space, access addresses 3FFC000H to 3FFEFFFH.
(2) Data space
With the V850E/RS1, there are sixty-four 64 MB address spaces on the 4 GB CPU address space.
Therefore, the least significant bit (bit 25) of a 26-bit address is sign-extended to 32 bits and allo-
cated as an address.
Example: An application example of wrap-around is shown below (µPD70F3402 / µPD70F3403 /
µPD70F3403A).
If R = r0 (zero register) is specified for the LD/ST disp16 [R] instruction, a range of addresses
00000000H ±32 KB can be addressed by sign-extended disp16. All the resources, including the
internal hardware, can be addressed by one pointer.
The zero register (r0) is a register fixed to 0 by hardware, and practically eliminates the need for
registers dedicated to pointers.
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Chapter 3 CPU Function
Figure 3-23: Wrap-Around Using µPD70F3402 / µPD70F3403 / µPD70F3403A
0001 FFFFH
0000 7FFFH
(R = )
0000 0000H
FFFF F000H
FFFF EFFFH
FFFF C800H
FFFF B000H
User's Manual U16702EE3V2UD00
Internal ROM area
32 KB
Internal peripheral
4 KB
I/O area
10 KB
Internal RAM area
16 KB