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C251 User's Guide
C251 Introduction Compiling Programs 
Language Extensions 
Keywords Memory Areas Program Memory Internal Data Memory External Data Memory Near Memory Far Memory Huge Memory SFR Memory Memory Models Tiny Model XTiny Model Small Model XSmall Model Large Model Memory Types Implicit Memory Types bdata code data ebdata far huge idata near xdata Data Types Special Function Registers sfr sfr16 sbit Bit-Addressable Objects bit Standard C Types void char int enum float double Type Modifiers signed unsigned short long Type Qualifiers const volatile Storage Classes auto register extern static Absolute Variable Location Pointers Memory Type in Pointer Declarations Pointer Conversions Function Declarations Memory Models Register Banks Interrupt Functions Reentrant Functions Alien (PL/M-51) Function Real-Time Function Tasks Preprocessor Advanced Programming Error Messages Library Reference AppendixProgram Memory
Program (CODE) memory is read only; it cannot be written to. Program memory may reside within the MCS® 251 MCU, it may be external, or it may be both, depending upon the 251 derivative and the hardware design.
- The 251 architecture supports up to 64K Bytes of program memory. However, program space can be expanded using code banking.
- Some devices offer a larger code space.
- Program code, including all functions and library routines, is stored in program memory.
- Constant variables may also be stored in program memory.
- The 251 executes programs stored in program memory only.
- Program memory may be accessed from your C programs using the code memory type specifier.
Note
- The code memory type is implemented for compatibility to the C51 compiler. Instead of code, you should use const near or const far. This generates typically better code and should be used in new 251 applications instead of the memory type code.
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