Program number and sequence numbers in CNC Programming - Step-by-Step Execution

Concept Flow - Program number and sequence numbers

Start Program

↓

Program Number: N100

↓

Sequence 1: N100 G01 X10 Y10

↓

Sequence 2: N110 G01 X20 Y20

↓

Sequence 3: N120 G01 X30 Y30

↓

End Program: M30

The CNC program starts with a program number, followed by sequence lines each with a sequence number, and ends with a program stop command.

Execution Sample

CNC Programming

N100 G01 X10 Y10
N110 G01 X20 Y20
N120 G01 X30 Y30
M30

This CNC program moves the tool to three positions in sequence and then ends.

Execution Table

Step	Line	Program Number	Sequence Number	Command	Action
1	N100 G01 X10 Y10	100	100	G01 X10 Y10	Move tool to X10 Y10
2	N110 G01 X20 Y20	100	110	G01 X20 Y20	Move tool to X20 Y20
3	N120 G01 X30 Y30	100	120	G01 X30 Y30	Move tool to X30 Y30
4	M30	100		M30	End program

💡 Program ends at M30 command.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
Program Number	None	100	100	100	100
Sequence Number	None	100	110	120	120
Tool Position	Unknown	(X10, Y10)	(X20, Y20)	(X30, Y30)	(X30, Y30)
Program State	Not started	Running	Running	Running	Ended

Key Moments - 3 Insights

Why does the program number stay the same across sequence lines?

The program number identifies the whole program and stays constant; sequence numbers change to order commands within the program, as shown in execution_table rows 1 to 3.

What happens if a sequence number is skipped or repeated?

Skipping or repeating sequence numbers can confuse the CNC controller's order of execution. Sequence numbers should increase logically, as seen in execution_table steps 1 to 3.

Why is the M30 command not given a sequence number?

M30 is a program stop command and usually does not have a sequence number; it signals the program end, as shown in execution_table step 4.

Visual Quiz - 3 Questions

Look at the execution table, what is the sequence number at step 2?

A 100

B 110

C 120

D None

💡 Hint

Check the 'Sequence Number' column in execution_table row 2.

At which step does the program end?

A Step 4

B Step 2

C Step 3

D Step 1

💡 Hint

Look for the M30 command in the 'Line' column in execution_table.

If the sequence number in step 3 was changed to N110, what would happen?

A Program number would change

B Program would run normally

C Sequence numbers would repeat, causing confusion

D Tool position would reset

💡 Hint

Refer to key_moments about sequence number repetition causing confusion.

Concept Snapshot

Program number (Nxxx) identifies the CNC program.
Sequence numbers (Nxxx) order commands inside the program.
Commands like G01 move the tool.
M30 ends the program.
Sequence numbers should increase logically.
Program number stays constant throughout.

Full Transcript

This lesson shows how a CNC program uses a program number and sequence numbers. The program starts with a program number, for example N100. Each line has a sequence number like N100, N110, N120 to order the commands. Commands like G01 move the tool to positions X10 Y10, X20 Y20, and X30 Y30 in order. The program ends with M30. The program number stays the same for all lines. Sequence numbers increase to keep commands in order. Repeating or skipping sequence numbers can cause confusion. The M30 command ends the program and usually has no sequence number. This helps CNC machines run the program step by step correctly.