Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 763)

Program Interrupt
Chapter 29
29-5
If an interrupt occurs during a block retrace, the interrupt will be
performed. The block retrace however will be aborted at that point and
no further retrace will be allowed. Block retrace will, however, still be
able to return any moves that have already been retraced before the
interrupt occurred.
During the execution of a milling cycle, if the interrupt is a delay type
(executed at the completion of the currently executing block), the
control will execute the interrupt after all motions generated by that
block are completed. If the interrupt type is immediate (executed as
soon as the interrupt signal is received), the control interrupts the
currently executing path.
There are two types of interrupts, type 1 and type 2. These are selected by
the L-word in the M96 block. L0 activates type 1 interrupts and L1, L2,
and L3 activate type 2 interrupts. Type 1 and type 2 interrupts are shown
in Figure 29.1 and Figure 29.2.
The key difference between a type 1 and a type 2 interrupt is the tool path
that is taken when the return from interrupt is made as programmed with
an M99 in the interrupt program.
Type 1 Interrupts
If no axis motion is generated by the interrupt program then the control
executes the interrupt program and then continues executing the part
program as normal regardless of the location that the interrupt program
was executed.
If axis motion is generated by the interrupt program then the control
returns the tool to the endpoint of the next fully unexecuted block and
continues executing the part program from this point.
29.3
Interrupt Types