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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 AppendixSpecial Function Registers
The 251 family of microcontrollers provides a distinct memory area for accessing Special Function Registers (SFRs). SFRs are used in your program to control timers, counters, serial I/Os, port I/Os, and peripherals. SFRs reside from address 0x80 to 0xFF and can be accessed as bits, bytes, and words. For more information about Special Function Registers, refer to the Intel 251/930 Embedded Controllers data book or other 251 data books.
Within the 251 family, the number and type of SFRs vary. Note that no SFR names are predefined by the C251 Compiler. However, declarations for SFRs are provided in include files.
The C251 Compiler provides a number of include files for various 251 derivatives. Each file contains declarations for the SFRs available on that derivative. Refer to 251 Special Function Register Include Files for more information about include files.
The C251 Compiler provides access to SFRs with the sfr, sfr16, and sbit data types.
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