 Cx51 User's Guide | |
| Home Products Events Support | |
On-Line Manuals
Cx51 User's Guide
Cx51 Introduction Compiling Programs Language Extensions Preprocessor Advanced Programming Customization Files
Startup Code Variable Initialization Code XBANKING.A51 Basic I/O Memory Allocation Optimizer Optimizer Options General Optimizations 8051-Specific Optimizations Global Register Coloring Segment Naming Conventions Data Objects Program Objects Parameters and Local Variables Interfacing C to Assembler Global Variables Function Parameters Passing in Memory Passing in Registers Function Return Values Using the SRC Directive Register Usage Overlaying Segments Small Model Example Compact Model Example Large Model Example Interfacing C programs to PL/M-51 Data Storage Formats Bit Variables 1-Byte Scalars 2-Byte Scalars 4-Byte Scalars Generic and Far Pointers Floating-point Numbers Floating-point Errors Absolute Memory Locations Absolute Access Macros Linker Location Controls The _at_ Keyword Debugging 8051 Derivatives Error Messages Library Reference AppendixInterfacing C to Assembler
You can easily interface your programs to routines written in 8051 Assembler. The A51 Assembler is an 8051 macro assembler that emits object modules in OMF51 format. By observing a few programming rules, you can call assembly routines from C and vice versa. Public variables declared in the assembly module are available for your C programs.
There are several reasons to call an assembly routine from your C program.
- You have assembly code already written that you wish to use.
- You need to improve the speed of a particular function.
- You want to manipulate SFRs or memory-mapped I/O devices directly from assembly.
This topic describes how to write assembly routines that can be directly interfaced to C programs.
For an assembly routine to be called from C, it must be aware of the parameter passing and return value conventions used in C functions. For all practical purposes, it must appear to be a C function.
| Contact Site Map Press Privacy | Copyright © 2008 Keil™, An ARM® Company. All rights reserved. |
