Syntax:
#BYTE id = x

Elements:
id is a valid C identifier,
x is a C variable or a constant

Purpose:
If the id is already known as a C variable then this will locate the variable at address x.  In this case the variable type does not change from the original definition.  If the id is not known a new C variable is created and placed at address x with the type int (8 bit)

Warning: In both cases memory at x is not exclusive to this variable.  Other variables may be located at the same location.  In fact when x is a variable, then id and x share the same memory location.

Examples:
#byte  status = 3

#byte  b_port = 6


struct  {

  short int r_w;

  short int c_d;

   int unused : 2;

  int data    : 4 ; } a _port;

#byte a_port = 5

...

a_port.c_d = 1;

呵呵 恩 知道了 是定义PORTA B C的地址 datasheet看少了