Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 767)

Program Interrupt
Chapter 29
29-9
If using a type 2 interrupt (L1, L2, or L3), remember that the control
remembers up to the first 4 blocks in the program and uses these to
retrace its moves back to the starting point of the interrupt program.
The control remembers up to 4 of the first moves or until a circular
block is executed. For details, see section 29.3 on interrupt types.
The interrupt program may contain a milling cycle in the interrupt.
These G codes are illegal in an interrupt program:
cutter compensation G codes G40, G41, and G42
coordinate system offsets G52, G92, and G92.1
Any inherent modality from the main program (such as a milling cycle,
or an active modal paramacro) will be temporarily canceled during the
execution of a interrupt program.
Only one interrupt may be executing at any given time. All 4 may be
active at once, but only one may be executing. This means that an
interrupt may not be executed during the execution of another interrupt.
END OF CHAPTER