SW500008 Microchip Technology, SW500008 Datasheet - Page 85

• Manufacturer Part Number: SW500008
• Description: PICC-18 STD
• Manufacturer: Microchip Technology
• Type: Compilerr
• Series: PIC18r

Specifications of SW500008

• Supported Families: PIC18
• Core Architecture: PIC
• Software Edition: Standard
• Kit Contents: Software And Docs
• Mcu Supported Families: PIC18
• Tool Function: Compiler
• Tool Type: Compiler
• Lead Free Status / RoHS Status: Not applicable / RoHS Compliant
• For Use With/related Products: PIC18 Series
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 015; 778-1001; 778-1001

C Language Features
3.11.2 Accessing C objects from within Assembly Code
Global C objects may be directly accessed from within assembly code using their name prepended
with an underscore character. For example, the object foo defined globally in a C module:
may be access from assembler as follows.
If the assembler is contained in a different module, then the GLOBAL assembler directive should be
used in the assembler code to make the symbol name available, as above. If the object is being
accessed from in-line assembly in another module, then an extern declaration for the object can be
made in the C code, for example:
This declaration will only take effect in the module if the object is also accessed from within C code.
If this is not the case then, an in-line GLOBAL assembler directive should be used. Care should be
taken if the object is defined in a bank other than 0. The address of a C object includes the bank
information which must be stripped before the address can be used in most PIC18 instructions. The
exceptions are the movff and lsfr instructions. Failure to do this may result in fixup errors issued
by the linker. If in doubt as to writing assembler which accesses C objects, write code in C which
performs a similar task to what you intend to do and study the assembler listing file produced by the
compiler.
T
To continue the previous example, here is a code snippet that declares the operation of
the assembler routine, then calls the routine.
extern unsigned int add(unsigned a, unsigned b);
void main(void)
{
}
int foo;
GLOBAL _foo
movwf
extern int foo;
UT RIAL
int a, result;
a = read_port();
result = add(5, a);
_foo
Mixing C and Assembler Code
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