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Cx51 User's Guide
Cx51 Introduction Compiling Programs Language Extensions Preprocessor Advanced Programming Customization Files
Startup Code Variable Initialization Code XBANKING.A51 Basic I/O Memory Allocation Optimizer Optimizer Options General Optimizations 8051-Specific Optimizations Global Register Coloring Segment Naming Conventions Data Objects Program Objects Parameters and Local Variables Interfacing C to Assembler Global Variables Function Parameters Passing in Memory Passing in Registers Function Return Values Using the SRC Directive Register Usage Overlaying Segments Small Model Example Compact Model Example Large Model Example Interfacing C programs to PL/M-51 Data Storage Formats Bit Variables 1-Byte Scalars 2-Byte Scalars 4-Byte Scalars Generic and Far Pointers Floating-point Numbers Floating-point Errors Absolute Memory Locations Absolute Access Macros Linker Location Controls The _at_ Keyword Debugging 8051 Derivatives Error Messages Library Reference AppendixSegment Naming Conventions
Objects generated by the Cx51 Compiler (program code, program data, and constant data) are stored in segments which are units of code or data memory. A segment may be relocatable or may be absolute. Each relocatable segment has a type and a name. This section describes the conventions used by the Cx51 Compiler for naming these segments.
Segment names include a module_name which is the name of the source file in which the object is declared. In order to accommodate a wide variety of existing software and hardware tools, all segment names are converted and stored in uppercase.
Each segment name has a prefix that corresponds to the memory type used for the segment. The prefix is enclosed in question marks (?). The following is a list of the standard segment name prefixes:
| Segment Prefix | Memory Type | Description |
|---|---|---|
| ?PR? | program | Executable program code |
| ?CO? | code | Constant data in program memory |
| ?BI? | bit | Bit data in internal data memory |
| ?BA? | bdata | Bit-addressable data in internal data memory |
| ?DT? | data | Internal data memory |
| ?FD? | far | Far memory (RAM space) |
| ?FC? | const far | Far memory (constant ROM space) |
| ?ID? | idata | Indirectly-addressable internal data memory |
| ?PD? | pdata | Paged data in external data memory |
| ?XD? | xdata | Xdata memory (RAM space) |
| ?XC? | const xdata | Xdata memory (constant ROM space) |
The segment name is assigned based on the memory model of the function.
Small Model Segment Naming Conventions
| Information | Segment Type | Segment Name |
|---|---|---|
| Program code | code | ?PR?function_name?module_name |
| Local variables | data | ?DT?function_name?module_name |
| Local bit variables | bit | ?BI?function_name?module_name |
Compact Model Segment Naming Conventions
| Information | Segment Type | Segment Name |
|---|---|---|
| Program code | code | ?PR?function_name?module_name |
| Local variables | pdata | ?PD?function_name?module_name |
| Local bit variables | bit | ?BI?function_name?module_name |
Large Model Segment Naming Conventions
| Information | Segment Type | Segment Name |
|---|---|---|
| Program code | code | ?PR?function_name?module_name |
| Local variables | xdata | ?XD?function_name?module_name |
| Local bit variables | bit | ?BI?function_name?module_name |
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