參數(shù)資料
型號(hào): LSI53C1000R
英文描述: LSI53C1000R Ultra160 SCSI controller
中文描述: LSI53C1000R Ultra160的SCSI控制器
文件頁數(shù): 22/166頁
文件大?。?/td> 1330K
代理商: LSI53C1000R
2-6
General Design Considerations
2.1.2.3 Generic Pointers vs. Memory-Specific Pointers
Due to the unique architecture of the 8051 and its derivatives, the
compiler provides two different types of pointers: generic pointers and
memory-specific pointers.
Generic pointers are always stored using three bytes. The first byte is for
the memory type, the second is for the high-order byte of the offset, and
the third is for the low-order byte of the offset. Generic pointers may be
used to access any variable regardless of its location in 8051 memory
space.
Memory-specific pointers always include a memory type specification in
the pointer declaration and always refer to a specific memory area.
Because the memory type is specified at compile-time, the memory type
byte required by generic pointers is not needed by memory-specific
pointers. Like generic pointers, the user may specify the memory area in
which a memory-specific pointer is stored. Memory-specific pointers may
be used to access variables in the declared 8051 memory area only.
Memory-specific pointers provide the most efficient method of accessing
data objects, but at the cost of reduced flexibility.
For more information, refer to your C compiler documentation,
specifically the sections covering directives and language extensions.
idata
indirectly addressable internal data memory; accessed across the full
internal address space (256 bytes).
pdata
paged (256 bytes) external data memory (16 Kbytes).
xdata
external data memory (refers to any location in the full 64 Kbytes of
external data memory).
code
program memory (16 Kbytes).
sfr
SFRs are declared in the same fashion as other variables. The only
difference is that the data type specified is
sfr
rather than
char
or
int
.
interrupt
an extension for standard C function declarations that indicates that
the function is an interrupt function.
using
specifies which register bank the function uses.
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