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UPD70F3114 Datasheet(PDF) 66 Page - NEC |
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UPD70F3114 Datasheet(HTML) 66 Page - NEC |
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66 / 692 page  CHAPTER 3 CPU FUNCTION 66 User’s Manual U15195EJ5V0UD 3.4.7 Recommended use of address space The architecture of the V850E/IA2 requires that a register that serves as a pointer be secured for address generation when accessing operand data in the data space. Operand data access from instruction can be directly executed at the address in this pointer register ±32 KB. However, because there is a limit to which general-purpose registers are used as a pointer register, by minimizing the deterioration of address calculation performance when changing the pointer value, the number of usable general-purpose registers for handling variables is maximized, and the program size can be saved. To enhance the efficiency of using the pointer in connection with of the memory map of the V850E/IA2, the following points are recommended. (1) Program space Of the 32 bits of the program counter (PC), the higher 6 bits are fixed to 0, and only the lower 26 bits are valid. Therefore, a contiguous 64 MB space, starting from address 00000000H, corresponds to the memory map of the program space. (2) Data space For the efficient use of resources that make use of the wrap-around feature of the data space, the continuous 16 MB address spaces 00000000H to 00FFFFFFH and FF000000H to FFFFFFFFH of the 4 GB CPU are used as the data space. With the V850E/IA2, a 256 MB physical address space is seen as 16 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. Example Application of wrap-around 00007FFFH (R =) 00000000H FFFFD800H FFFF8000H Internal ROM area On-chip peripheral I/O area FFFFF000H FFFFEFFFH FFFFBFFFH FFFFD7FFH FFFFC000H Internal RAM area 32 KB 4 KB 6 KB 16 KB 0001FFFFH When R = r0 (zero register) is specified with the LD/ST disp16 [R] instruction, an addressing range of 00000000H ±32 KB can be referenced by the sign-extended disp 16. By mapping the external memory in the 16 KB area in the figure, all resources of internal hardware can be accessed with one pointer. The zero register (r0) is a register set to 0 by the hardware, and eliminates the need for additional registers for the pointer. |
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