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C251 User's Guide
C251 Introduction Compiling Programs Language Extensions Preprocessor 
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Startup Code Variable Initialization Code Basic I/O Memory Allocation Optimizer General Optimizations 251-Specific Optimizations Options for Code Generation Global Register Coloring Segment Naming Conventions Segment Types Initialization Segments Function Symbols Parameter Passing Symbols Hardware Stack Calculating Stack Size Interfacing C Programs to Assembler Global Variables Function Parameters Passing in Memory Passing in Registers Function Return Values Using the SRC Directive Register Usage Overlaying Segments TINY Model XTINY Model SMALL Model XSMALL Model LARGE Model Data Storage Formats Bit Variables 1-Byte Scalars 2-Byte Scalars 4-Byte Scalars Floating-point Numbers Floating-point Errors Double Numbers Double Errors Absolute Memory Locations Absolute Access Macros Linker Location Controls The _at_ Keyword Debugging Error Messages Library Reference AppendixSegment Naming Conventions
Objects generated by the C251 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 C251 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 Class | Memory Type | Description |
|---|---|---|---|
| ?PR? | CODE or ECODE | program | Executable program code |
| ?CO? | CODE | code | Constant data in program memory |
| ?BI? | BIT | bit | Bit data in internal data memory |
| ?BA? | BDATA | bdata | Bit-addressable data in internal data memory |
| ?DT? | DATA | data | Internal data memory with 8-bit addressing |
| ?ED? | EDATA | near | Variables with 16-bit addressing |
| ?EA? | EBDATA | ebdata | Extended 251 bit-addressable variables |
| ?EB? | EBIT | bit ebdata | Extended 251 bits |
| ?FD? | HDATA | far | Far memory (RAM space) |
| ?FC? | HCONST | const far | Far memory (constant ROM space) |
| ?HD? | HDATA | huge | Huge variables (no size limitation) |
| ?HC? | HCONST | const huge | Huge constants (no size limitation) |
| ?ID? | IDATA | idata | Indirectly addressable internal data memory |
| ?NC? | NCONST | const near | Constants with 16-bit addressing |
| ?PD? | PDATA | pdata | Paged data in external data memory |
| ?XD? | XDATA | xdata | Xdata memory (RAM space) |
| ?XC? | XDATA | const xdata | Xdata memory (constant ROM space) |
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