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UPD784938 Datasheet(PDF) 81 Page - NEC |
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UPD784938 Datasheet(HTML) 81 Page - NEC |
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81 / 733 page  81 CHAPTER 3 CPU ARCHITECTURE Preliminary User’s Manual U13987EJ1V0UM00 3.4.2 Special function register (SFR) area The on-chip peripheral hardware special function registers (SFRs) are mapped onto the area from 0FF00H to 0FFFFH (see Figures 3-1, 3-2, 3-3, and 3-4). The area from 0FFD0H to 0FFDFH is mapped as an external SFR area, and allows externally connected peripheral I/Os, etc., to be accessed in external memory expansion mode (specified by the memory expansion mode register (MM)) by the ROM- less product or on-chip ROM products. Caution Addresses onto which SFRs are not mapped should not be accessed in this area. If such an address is accessed by mistake, the CPU may become deadlocked. A deadlock can only be released by reset input. Remark The addresses in this text are those that apply when the LOCATION 0 instruction is executed. When the LOCATION 0FH instruction is executed, 0F0000H should be added to the values shown in the text. 3.4.3 External SFR area In µPD784938 Subseries products, the 16-byte area from 0FFD0H to 0FFDFH in the SFR area (when the LOCATION 0 is executed; 0FFFD0H to 0FFFDFH when the LOCATION 0FH instruction is executed) is mapped as an external SFR area. When the external memory expansion mode is set in a ROM-less product or on-chip ROM product, externally connected peripheral I/Os, etc., can be accessed using the address bus or address/data bus, etc. As the external SFR area can be accessed by SFR addressing, peripheral I/O and similar operations can be performed easily, the object size can be reduced, and macro service can be used. Bus operations for accesses to the external SFR area are performed in the same way as for ordinary memory accesses. 3.5 External Memory Space The external memory space is a memory space that can be accessed in accordance with the setting of the memory expansion mode register (MM). It can store programs, table data, etc., and can have peripheral I/O devices allocated to it. |
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