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XC2200 Derivatives
System Units (Vol. 1 of 2)
Memory Organization
User’s Manual
3-15
V2.1, 2008-08
MemoryX2K, V1.3
3.6
IO Areas
The following areas of the XC2200’s address space are marked as IO area:
•
The
external IO area
is provided for external peripherals (or memories) and also
comprises the on-chip LXBus-peripherals, such as the CAN or USIC modules. It is
located from 20’0000
H
to 3F’FFFF
H
(2 Mbytes).
•
The
internal IO area
provides access to the internal peripherals and is split into three
blocks:
– The SFR area, located from 00’FE00
H
to 00’FFFF
H
(512 bytes).
– The ESFR area, located from 00’F000
H
to 00’F1FF
H
(512 bytes).
– The XSFR area, located from 00’E000
H
to 00’EFFF
H
(4 Kbytes).
Note: The external IO area supports real byte accesses. The internal IO area does not
support real byte transfers, the complementary byte is cleared when writing to a
byte location.
The IO areas have special properties, because peripheral modules must be controlled
in a different way than memories:
•
Accesses are not buffered and cached, the write back buffers and caches are not
used to store IO read and write accesses.
•
Speculative reads are not executed, but delayed until all speculations are solved (e.g.
pre-fetching after conditional branches).
•
Data forwarding is disabled, an IO read access is delayed until all IO writes pending
in the pipeline are executed, because peripherals can change their internal state after
a write access.