The PLOT kernal routine is located at $FFF0 (65520).
When this routine is called, it will get or set the cursor position based on the status of the Carry status flag.
If the Carry flag is cleared before calling the function, then the cursor will be set to the position specified by in registers X and Y. The value of X and Y are preserved, but the value in the accumulator will be overwritten.
If the Carry flag is set before calling the function, then the cursor position will be returned in registers X and Y. The value in the accumulator will be preserved.
The X register represents the row, and the Y register represents the column of the cursor.
Real address of Kernal routine: $E50A.