User’s Manual U11969EJ3V0UM00
63
CHAPTER 3 CPU FUNCTIONS
(3) Peripheral I/O area
A 4-Kbyte area of addresses FFF000H to FFFFFFH is reserved as a peripheral I/O area. The V854 is provided
with a 1-Kbyte area of addresses FFF000H to FFF3FFH as a physical peripheral I/O area, and the image of
FFF000H to FFF3FFH can be seen on the rest of the area (FFF400H to FFFFFFH).
Peripheral I/O registers associated with the operation mode specification and the state monitoring for the on-
chip peripherals are all memory-mapped to the peripheral I/O area. Program fetches are not allowed in this
area.
Cautions 1. The least significant bit of an address is not decoded since all registers reside on an
even address. If an odd address (2n + 1) in the peripheral I/O area is referenced, the
register at the next lowest even address (2n) will be accessed.
2. If a register that can be accessed in byte units is accessed in half-word units, the higher
8 bits become undefined, if the access is a read operation. If a write access is made,
only the data in the lower 8 bits is written to the register.
3. If a register with n address that can be accessed only in halfword units is accessed with
a word operation, the operation is replaced with two halfword operations. The first
operation (lower 16 bits) accesses to the register with n address and the second
operation (higher 16 bits) accesses to the register with n + 2 address.
4. If a register with n address that can be accessed in word units is accessed with a word
operation, the operation is replaced with two halfword operations. The first operation
(lower 16 bits) accesses to the register with n address and the second operation (higher
16 bits) accesses to the register with n + 2 address.
5. Addresses that are not defined as registers are reserved for future expansion. If these
addresses are accessed, the operation is undefined and not guaranteed.
XXFFFFFFH
XXFFFC00H
XXFFFBFFH
XXFFF800H
XXFFF7FFH
XXFFF400H
XXFFF3FFH
XXFFF000H
Image
Image
Image
Physical peripheral I/O
3FFH
000H
Image
Peripheral I/O
Summary of Contents for V854 UPD703006
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