Thanks for the tip on how to define them. I have put all of my functions and variable defines in .c and protoypes and declarations in .h files.

Every thing works except for the functions for writing data to an LCD. The initialisation function in the same file works ok though? All of the functions worked before they were seperated.

here is most of my header file, is the a prblem with the way I am doing it?

#ifndef _LCD_
#define _LCD_

extern void LCD_init (void);
extern void LCD_write_cmd (byte cmd);
extern void LCD_write_data (byte disp);
extern void LCD_write_data_string (byte *string1);

#endif


this has been #include'd in my main c file.