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XC2200 Derivatives
System Units (Vol. 1 of 2)
Architectural Overview
User’s Manual
2-9
V2.1, 2008-08
ArchitectureX22, V1.1
2.1.6
Interfaces to System Resources
The CPU of the XC2200 interfaces to the system resources via several bus systems
which contribute to the overall performance by transferring data concurrently. This
avoids stalling the CPU because instructions or operands need to be transferred.
The Dual Port RAM (DPRAM) is directly coupled to the CPU because it houses the
global register banks. Transfers from/to these locations affect the performance and are,
therefore, carefully optimized.
The Program Management Unit (PMU)
controls accesses to the on-chip program
memory blocks such as the ROM/Flash module and the Program/Data RAM (PSRAM)
and also fetches instructions from external memory.
The 64-bit interface between the PMU and the CPU delivers the instruction words, which
are requested by the CPU. The PMU decides whether the requested instruction word
has to be fetched from on-chip memory or from external memory.
The Data Management Unit (DMU)
controls accesses to the on-chip Data RAM
(DSRAM), to the on-chip peripherals connected to the peripheral bus, and to resources
on the external bus. External accesses (including accesses to peripherals connected to
the on-chip LXBus) are executed by the External Bus Controller (EBC).
The 16-bit interface between the DMU and the CPU handles all data transfers
(operands). Data accesses by the CPU are distributed to the appropriate buses
according to the defined address map.
PMU and DMU are directly coupled to perform cross-over transfers with high speed.
Crossover transfers are executed in both directions:
•
PMU via DMU:
Code fetches from external locations are redirected via the DMU to
EBC. Thus, the XC2200 can execute code from external resources. No code can be
fetched from the Data RAM (DSRAM).
•
DMU via PMU:
Data accesses can also be executed to on-chip resources controlled
by the PMU. This includes the following types of transfers:
– Read a constant from the on-chip program ROM/Flash
– Read data from the on-chip PSRAM
– Write data to the on-chip PSRAM (required prior to executing out of it)
– Program/Erase the on-chip Flash memory