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XC2200 Derivatives
System Units (Vol. 1 of 2)
Memory Organization
User’s Manual
3-2
V2.1, 2008-08
MemoryX2K, V1.3
The XC2200 provides a total addressable memory space of 16 Mbytes. This address
space is arranged as 256 segments of 64 Kbytes each, and each segment is again
subdivided into four data pages of 16 Kbytes each (see
Bytes are stored at even or odd byte addresses. Words are stored in ascending memory
locations with the low byte at an even byte address being followed by the high byte at
the next odd byte address (“little endian”). Double words (code only) are stored in
ascending memory locations as two subsequent words. Single bits are always stored in
the specified bit position at a word address. Bit position 0 is the least significant bit of the
byte at an even byte address, and bit position 15 is the most significant bit of the byte at
the next odd byte address. Bit addressing is supported for a part of the Special Function
Registers, a part of the internal RAM and for the General Purpose Registers.
Figure 3-2
Storage of Words, Bytes and Bits in a Byte Organized Memory
Note: Byte units forming a single word or a double word must always be stored within
the same physical (internal, external, ROM, RAM) and organizational (page,
segment) memory area.
xxxx’xxxF
H
xxxx’xxx0
H
xxxx’xxx1
H
xxxx’xxx2
H
xxxx’xxx3
H
xxxx’xxx4
H
xxxx’xxx5
H
xxxx’xxx6
H
xxxx’xxx7
H
xxxx’xxx8
H
xxxx’xxx9
H
xxxx’xxxA
H
Double Word (Low Byte)
Double Word (Second Byte)
Double Word (Third Byte)
Double Word (High Byte)
Word (Low Byte)
Word (High Byte)
Byte
Byte
7
6
0
… Bits ...
imb_endianess.vsd:byte_orga