XC2000 datasheet(79/647 Pages) INFINEON

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XC2000 Derivatives

System Units (Vol. 1 of 2)

Memory Organization

Preliminary

User’s Manual

3-17

V1.0, 2007-06

MemoryX2K, V1.1

3.8

Crossing Memory Boundaries

The address space of the XC2000 is implicitly divided into equally sized blocks of

different granularity and into logical memory areas. Crossing the boundaries between

these blocks (code or data) or areas requires special attention to ensure that the

controller executes the desired operations.

Memory Areas are partitions of the address space assigned to different kinds of

memory (if provided at all). These memory areas are the SFR areas, the on-chip

program or data RAM areas, the on-chip ROM/Flash (if available), the on-chip LXBus-

peripherals (if integrated), and the external memory.

Accessing subsequent data locations which belong to different memory areas is no

problem. However, when executing code, the different memory areas must be switched

explicitly via branch instructions. Sequential boundary crossing is not supported and

leads to erroneous results.

Note: Changing from the external memory area to the on-chip RAM area takes place

within segment 0.

Segments are contiguous blocks of 64 Kbytes each. They are referenced via the Code

Segment Pointer CSP for code fetches and via an explicit segment number for data

accesses overriding the standard DPP scheme.

During code fetching, segments are not changed automatically, but rather must be

switched explicitly. The instructions JMPS, CALLS and RETS will do this.

In larger sequential programs, make sure that the highest used code location of a

segment contains an unconditional branch instruction to the respective following

segment to prevent the pre-fetcher from trying to leave the current segment.

Data Pages are contiguous blocks of 16 Kbytes each. They are referenced via the data

page pointers DPP3 … DPP0 and via an explicit data page number for data accesses

overriding the standard DPP scheme. Each DPP register can select one of the possible

1024 data pages. The DPP register which is used for the current access is selected via

the two upper bits of the 16-bit data address. Therefore, subsequent 16-bit data

addresses which cross the 16-Kbytes data page boundaries will use different data page

pointers, while the physical locations need not be subsequent within memory.

XC2000 Datasheet(PDF) 79 Page - Infineon Technologies AG