Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 283)

Introduction to Programming
Chapter 10
10-9
Each block in a part program can be assigned a sequence number to
distinguish one block from another. Sequence numbers begin with an N
address followed by a one to five digit numeric value.
Sequence numbers can be assigned at random to specific blocks or to all
blocks if desired. Blocks assigned sequence numbers can be called later by
designating their sequence number. Sequence numbers are necessary to
make program jumps and to specify a block for paramacro calls and
returns.
Below is an example of two blocks with sequence numbers 10000 and
10010.
Example 10.5
Blocks With Sequence Numbers
N10000 X5. Z4. ;
N10010 X2. Z2. ;
Typically when assigning sequence numbers to blocks the N--word comes
first in the block except when designating block delete (see section 10.2.4).
It is not necessary to program the N--word first in the block, the control
will still find it for jumps; however, it will not be found for renumber
operations.
If more than one N--word is in a block, the control only uses the first
N--word encountered for that block’s number.
Different blocks may be assigned the same sequence number. If this
number is called by a “GOTO” or some other command the first block
found by the control with the required sequence number calling block is
used. Note that the control searches for the sequence number in the
forward direction (from the calling block) first. Then it searches in the
reverse direction (from the calling block). How the control reacts if the
sequence number is not found is determined by the specific operation
being used.
The control has a programming feature that will renumber existing
sequence numbers or assign all block sequence numbers. For details refer
to chapter 5.
10.2.2
Sequence Numbers