Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 305)

Introduction to Programming
Chapter 10
10-31
The basic M--codes for the control are shown in Table 10.F. A part
program block may contain as many basic M--codes as desired. If more
than one M--code from any modal group is programmed in the same block,
the rightmost M--code in that block for that modal group is the active
M--code for the block.
The system installer may have defined additional M--codes in PAL. Up to
four of these PAL M--codes may be activated in any one block. If more
then four PAL M--codes are programmed in any one block the right most
four in that block are activated. Other PAL M--codes in the block are
ignored. Refer to documentation provided by the system installer for
details on PAL defined M--codes and their operation. You may program as
one basic control M--code from each modal group with up to four PAL
M--codes in any one block.