MOVX

a very good reason to be hacking with absolute addresses

One of the most common good reasons is if you have hardware memory-mapped into the external data space. So, to write to a particular address, you must write to a particular xdata address.

In this case, you could use the _at_ directive to locate a variable. Or, you could use a C pointer.

volatile U8 xdata myReg _at_ 0xF000;

#define XdataReg(addr) (*((volatile xdata U8*)(addr)))
#define myReg XdataReg(0xF000)

myReg = 0;
myReg |= 1;

a very good reason to be hacking with absolute addresses

One of the most common good reasons is if you have hardware memory-mapped into the external data space. So, to write to a particular address, you must write to a particular xdata address.

In this case, you could use the _at_ directive to locate a variable. Or, you could use a C pointer.

volatile U8 xdata myReg _at_ 0xF000;

#define XdataReg(addr) (*((volatile xdata U8*)(addr)))
#define myReg XdataReg(0xF000)

myReg = 0;
myReg |= 1;

"One of the most common good reasons is if you have hardware memory-mapped into the external data space."

Of course.

XBYTE is effectively just a "magic number" address - hence I prefer using _at_.

Using _at_ automatically informs the tools that there is something at the specified location; using "magic number" addresses - whether via XBYTE or a pointer - hides this from the tools, so they have no reason to know that the address is "reserved"!