C51: Mixing C and Assembly

Information in this article applies to:

• C51 Version 6.02
• µVision Version 2.06

QUESTION

Do you have any examples of how to mix C and assembly?

ANSWER

The following example program shows how to mix C and assembly in your 8051 programs.

This example starts with a MAIN C function which calls a routine in assembly which then calls a C function.

The MAIN C module appears as follows:

extern void a_func (void);

void main (void)
{
a_func ();
}

The function a_func is an assembly routine:

NAME    A_FUNC

?PR?a_func?A_FUNC    SEGMENT CODE
        EXTRN   CODE (c_func)
        PUBLIC  a_func

        RSEG    ?PR?a_func?A_FUNC
a_func:
        USING   0
        LCALL   c_func
        RET

        END

Note that this assembly routine calls c_func which is a C function:

void c_func (void)
{
}

The actual code for the assembly module was generated using the SRC pragma and the following C source file:

extern void c_func (void);

void a_func (void)
{
c_func ();
}

You may download C2ASM2C.ZIP from the Keil web site.

SEE ALSO

• C51: Calling Assembly Routines from C
• A51: Calling C Functions From Assembly
• GENERAL: How to Create Assembly Files from C Files
• C51: Adding C Functions to Existing Assembler Code

Last Reviewed: Thursday, February 25, 2021