C167CS-4RM datasheet(49/517 Pages) INFINEON

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C167CS

Derivatives

Memory Organization

User’s Manual

3-12

V2.0, 2000-07

3.5

Crossing Memory Boundaries

The address space of the C167CS 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 that represent different kinds of

memory (if provided at all). These memory areas are the internal RAM/SFR area, the

internal ROM/Flash/OTP (if available), the on-chip X-Peripherals (if integrated) and the

external memory.

Accessing subsequent data locations that 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 internal RAM/SFR area takes

place within segment 0.

Segments are contiguous blocks of 64 KByte 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 prefetcher from trying to leave the current segment.

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

page pointers DPP3 … 0 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 that is used for the current access is selected via the

two upper bits of the 16-bit data address. Subsequent 16-bit data addresses that cross

the 16 KByte data page boundaries therefore will use different data page pointers, while

the physical locations need not be subsequent within memory.

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