C51 interrupt routine

In C51 interrupt routine function
attribute USING Rn what purpose it will serve.
Used correctly it switches the register bank to one that is neither used by the body of the code nor an interrupt with higher priority. My "standard" is main in bank 0, low priority ints in bank 1 and high priority ints in bank 2.
If i am not using the same as in main (added for clarification),what will happen in ISR.Pls explain me.
Nothing, everything will work as your code says. But if you are using the same in main and an ISR that affect ANY register, your code will show erratic behaviour.

Erik

In C51 interrupt routine function
attribute USING Rn what purpose it will serve.
Used correctly it switches the register bank to one that is neither used by the body of the code nor an interrupt with higher priority. My "standard" is main in bank 0, low priority ints in bank 1 and high priority ints in bank 2.
If i am not using the same as in main (added for clarification),what will happen in ISR.Pls explain me.
Nothing, everything will work as your code says. But if you are using the same in main and an ISR that affect ANY register, your code will show erratic behaviour.

Erik