 Cx51 User's Guide | |
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Cx51 User's Guide
Cx51 Introduction Compiling Programs Language Extensions
Keywords Memory Areas Program Memory Internal Data Memory External Data Memory Far Memory SFR Memory Memory Models Small Model Compact Model Large Model Memory Types bdata code data far idata pdata 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 Generic Pointers Memory-Specific Pointers Pointer Conversions Abstract Pointers Function Declarations Parameters and the Stack Parameters and Registers Return Values Memory Models Register Banks Register Bank Access Interrupt Functions Reentrant Functions Alien (PL/M-51) Function Real-Time Function Tasks Preprocessor Advanced Programming 8051 Derivatives Error Messages Library Reference AppendixReturn Values
MCU registers are always used for function return values. The following table lists the return types and the registers used for each.
| Return Type | Registers | Storage Format |
|---|---|---|
| bit | Carry Flag | |
| char, unsigned char, 1-byte ptr | R7 | |
| int, unsigned int, 2-byte ptr | R6 & R7 | MSB in R6, LSB in R7 |
| long, unsigned long | R4-R7 | MSB in R4, LSB in R7 |
| float | R4-R7 | 32-Bit IEEE format |
| generic ptr | R1-R3 | Memory type in R3, MSB R2, LSB R1 |
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