If the functions are in the same file, make it 'static'
http://www.8052.com/forum/read.phtml?id=72566

If the functions are in different files, you need a definition in exactly one file, and corresponding 'extern' declarations in all other files that need access to it.
This is best accomplished by use of a Header File

If you just need to see the value of the variable (not change the variable itself), you can pass it as a parameter:

void main(void) 
{ 
   unsigned char x; 

   x = 0x31; 

   dosomething( x );
} 

void dosomething( unsigned char xx ) 
{ 
   unsigned char y; 

   y = xx; 
}

If you want to be able to change the value of the variable without making it global you can, with great care, use a Pointer:

void main(void) 
{ 
   unsigned char x; 

   x = 0x31; 

   dosomething( &x );
} 

void dosomething( unsigned char *px ) 
{ 
   unsigned char y; 

   y = 23;

   *px = y; 
}

NOTE: This example is purely for the purposes of illustrating that it can be done; I am not saying that this is a good example of what you should do!


Absolutely!
None of this is specific to the 8051 - it is all perfectly standard 'C' language basics.


Perhaps KR shold read K&R...? ;-)