75
Chapter 3
CPU Function
Preliminary User’s Manual U15839EE1V0UM00
3.5.2 Recommended use of address space
The architecture of the V850E/CA2 requires that a register is utilized for address generation when
accessing operand data in the data space. Operand data access from instruction can be directly exe-
cuted at the address in this pointer register ±32 KB. However, the use of general registers as pointer
registers decreases the number of usable general registers for handling variables, but minimizes the
deterioration of address calculation performance when changing the pointer value and minimizes the
program size as well.
To enhance the efficiency of using the pointer in consideration of the memory map of the V850E/CA2,
the following points are recommended:
(1)
Program space
Of the 32 bits of the PC (program counter), the higher 6 bits are fixed to zero (0), and only the
lower 26 bits are valid. Therefore, a contiguous 64 MB space, starting from address 0000 0000H,
unconditionally corresponds to the memory map of the program space.
(2)
Data space
For the efficient use of resources to be performed through the wrap-around feature of the data
space, the continuous 16 MB address spaces 0000 0000H to 00FF FFFFH and FF00 0000H to
FFFF FFFFH of the 4 GB CPU address space are used as the data space. With the V850E/CA2,
64 MB physical address space is seen as 64 images in the 4 GB CPU address space. The highest
bit (bit 25) of this 26-bit address is assigned as address sign-extended to 32 bits.
Figure 3-14:
Example Application of wrap-around (µPD703129)
When R = r0 (zero register) is specified with the LD/ST disp16 [R] instruction, an addressing range
of 0000 0000H ±32 KB can be referenced with the sign-extended, 16-bit displacement value.
The zero register (r0) is a register set to 0 by hardware, and eliminates the need for additional
registers for the pointer.
0000 7FFFH
(R=)0000 0000H
FFFF C000H
External ROM area
Internal peripheral
I/O area
FFFF F000H
FFFF EFFFH
FFFF BFFFH
FFFF 8000H
Internal RAM area
+32 Kbytes
4 Kbytes
16 Kbytes
12 Kbytes
-32 Kbytes
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