sfr

SFRs are declared in the same fashion as other C variables. The only difference is that the data type specified is sfr rather than char or int. For example:

sfr P0 = 0x80;    /* Port-0, address 80h */
sfr P1 = 0x90;    /* Port-1, address 90h */
sfr P2 = 0xA0;    /* Port-2, address 0A0h */
sfr P3 = 0xB0;    /* Port-3, address 0B0h */

P0, P1, P2, and P3  are the SFR name declarations. Names for sfr variables are defined just like other C variable declarations. Any symbolic name may be used in an sfr declaration.

The address specification after the equal sign (=) must be a numeric constant. (Expressions with operators are not allowed.) This constant expression must lie in the SFR address range (0x80 to 0xFF).