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CHAPTER 23 LOCAL BUS INTERFACE FUNCTIONS
User’s Manual U12697EJ3V0UM
23.3 Memory Map for External Memory Expansion
Figures 23-4 and 23-5 show the memory map during memory expansion. Even during memory expansion, an
external device at the same address as the internal ROM area, internal RAM area, or SFR area (except for the external
SFR area (0FFD0H to 0FFDFH)) cannot be accessed. If these areas are accessed, the memory and SFR in
µ
PD784225 are accessed with priority, and the ASTB, RD, and WD signals are not output (remaining at the inactive
level). The output level of the address bus remains at the previous output level. The output of the address/data bus
has a high impedance.
Except in the 1 MB expansion mode, an address for external output is output in the state that masked the high
order side of the address set by the program.
<Example 1>
When address 54321H is accessed in the program in the 256 KB expansion mode, the address that is output
becomes 14321H.
<Example 2>
When address 67821H is accessed in the program in the 256 KB expansion mode, the address that is output
becomes 27821H.
Содержание mPD784225 Series
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