I think Alfredo is right, store it in the on-chip registers rather than the LCD RAM... 2nd way is too slow and long-winded

Simple:
one method is that whatever you receive from the PC you store in some register or memory location
i.e.
-i/p char string data from PC
-store data in some register/RAM
(I suppose you are already doing this)
-Write to LCD from this RAM
-If interrupt occurs, display the new text
-At the end of interrupt restore earlier message to LCD

Another method, slower and less efficient,is:
-O/P data to LCD
-when interrupt occurs, read from LCD buffer and store into 8051 RAM
-display new data
-At the end of interrupt display old data

kundi