#define statement assigning addresses

[glennpl]

I dont understand the pointers or the parenthesis. Please help

#define PORTA *(unsigned char volatile *)(0x0000) 

[MikeyBoy]

(unsigned char volatile *) is a C-style cast. So:

(unsigned char volatile *)(0x0000)

is casting the literal value 0x0000 to a pointer to an unsigned char volatile.

[S G H]

You're basically saying you want to access the byte 0 in the memory.