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LX51 User's Guide
LX51 Introduction Purpose of the Linker 
Combining Modules Searching Libraries Combining Segments Locating Segments Overlaying Data Memory Resolving Externals Calculating Addresses Generating an Object File Generating a Listing File Memory Classes BIT, DATA, and IDATA CODE and CONST XDATA HCONST HDATA Classic 8051 Devices Extended 8051 Devices NXP 51MX Devices Segments 
Linking Programs Locating Program Objects Data Overlaying Code Banking Real-Time Programs Error MessagesMemory Classes
A class is an arbitrarily ordered collection of segments that share a common attribute. The purpose of a class is to allow manipulation of a number of segments using only the class name. For instance, the code objects from all modules in a program are combined into the CODE class while the xdata objects are combined into the XDATA class.
You may use the CLASSES linker directive to specify the address range for a class rather than specifying the addresses for each segment individually.
The following default classes are generated automatically by the linker. However, any number of user classes may be created and linked.
| Memory Class | Address Range | Description |
|---|---|---|
| BIT | I:20h.0-I:2Fh.7 | Bit memory limited to 16 Bytes. |
| CODE | C:0000h-C:0FFFFh | Code memory limited to 64 KBytes. |
| CONST | C:0000h-C:0FFFFh | Constant data limited to 64 KBytes. |
| DATA | D:00h-D:7Fh | Variable data limited to 128 Bytes and accessed using the MOV instructions. |
| HCONST | C:000000h-C:0FFFFFFh | Constant data limited to 16 MBytes. |
| HDATA | X:000000h-X:0FFFFFFh | Variable data limited to 16 MBytes. |
| IDATA | I:00h-I:0FFh | Variable data limited to 256 Bytes and accessed using the MOV @Rx instructions. |
| XDATA | X:0000h-X:0FFFFh | Variable data limited to 64 KBytes and accessed using the MOVX instruction. |
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