Advanced CNC Subprograms and Loops: G22, G23, M98, M99, and Conditional Logic with Real Macros

CNC machines aren’t just motion devices — they’re programmable computers capable of conditional logic, looping, and modular routines.
By mastering subprograms and logic commands like G22, G23, M98, M99, and macro conditions (IF/WHILE), you can automate complex repetitive machining with clean, reusable code.

This guide provides real-world examples from Fanuc, Haas, Siemens, and Heidenhain systems.

---

📌 1. What Are CNC Subprograms?

Subprograms are reusable blocks of G-code stored in the control’s memory, usually named as:

O9000 – O9999

They are called using:

M98 Pxxxx Lnn

and ended with:

M99

Command	Function
M98	Call a subprogram
Pxxxx	Subprogram number
Lnn	Number of repetitions
M99	Return to main program or loop back

---

📌 2. Basic Fanuc Example — Subprogram Call

Main Program (O1000)

%
O1000 (MAIN PROGRAM)
G90 G17 G21
M98 P2000 L3
M30
%

Subprogram (O2000)

%
O2000 (DRILL CYCLE)
G81 Z-15. R2. F100
G80
M99
%

Executes subprogram O2000 three times using L3.

---

📌 3. Haas Example — Multi-Hole Pattern with M98/M99

%
O3000 (HAAS MAIN)
T01 M06
M98 P4000 L5
M30
%

%
O4000 (SUBPROGRAM)
G81 X[#100] Y[#101] Z-20. R2. F150
#100 = [#100 + 20]
M99
%

Drills five holes 20 mm apart in X using a loop variable.

---

📌 4. Nested Subprogram Calls (Fanuc)

Subprograms can call other subprograms:

M98 P2000
...
O2000
M98 P3000
M99
O3000
(SECONDARY SUBROUTINE)
M99

Enables modular machining — for example, one subprogram for drilling, another for tapping.

---

📌 5. M99 — Return or Loop Back

Context	Behavior
Inside subprogram	Returns to caller
Inside main program	Loops to start

Example:

O5000
G01 X100.
M99

When executed directly, M99 loops infinitely (use with caution).

---

📌 6. G22 & G23 — Axis Limit Control

Code	Function
G22	Enable soft limit check
G23	Disable soft limit check

Example:

G22 X-100. X100.
G00 X150.  (ALARM)
G23
G00 X150.  (NOW OK)

G22 protects from exceeding the soft travel range — ideal for automation and unmanned cycles.

---

📌 7. WHILE / END Loop — Repetition Without M98

#100 = 0
WHILE [#100 LT 5] DO1
G81 X[#100*20] Y0 Z-10. R2. F150
#100 = [#100 + 1]
END1
M30

Repeats drilling operation 5 times without subprogram call — fully contained logic loop.

---

📌 8. IF / GOTO Conditional Logic

#500 = 45
IF [#500 GT 50] GOTO 100
G01 Z-10. F100
N100 G01 Z-20. F150

Executes different depths based on variable condition — foundational to CNC decision-making.

---

📌 9. Real Example — Automatic Pattern Generator

#100 = 0
#101 = 5  (HOLE COUNT)
#102 = 25 (SPACING)

WHILE [#100 LT #101] DO1
M98 P3000
#100 = [#100 + 1]
END1
M30

O3000
G81 X[#100 * #102] Y0 Z-20. R2. F120
G80
M99

Dynamically creates hole patterns based on variables — zero code duplication.

---

📌 10. Siemens Example — LBL CALL & GOTO

LBL 1
CYCLE83(DEPTH=-20, PECK=5)
LBL CALL 1 REP=5
LBL 0

Equivalent to M98 loop logic — Siemens uses LBL (label) instead of O numbers.

---

📌 11. Heidenhain Example — CALL LBL

LBL 1
CYCL DEF 200 DRILLING Q201=-20 Q206=+150
LBL CALL 1 REP4
LBL 0

Executes subroutine 4 times — Heidenhain subprogram syntax is clean and structured.

---

📌 12. Mazak Example — Smooth Control Subprogram

M98 P8001 L10
O8001
G81 Z-10. R2. F100
M99

Standard ISO-compatible M98/M99 subroutine control in Mazak SmoothX systems.

---

📌 13. Conditional Tool Change Macro (Fanuc)

#500 = [#500 + 1]
IF [#500 GE 10] THEN #3006 = 1 (TOOL CHANGE REQUIRED)

After 10 cycles, display message to change the tool — perfect for unattended machining.

---

📌 14. Recursive Subprogram Example (Advanced)

O7000
#100 = [#100 + 1]
IF [#100 GT 5] GOTO 100
G01 X[#100*10] F200
M98 P7000
N100 M99

Calls itself recursively until the condition breaks — caution: ensure escape logic exists.

---

📌 15. Preventing Machine Overtravel with G22/G23

G22 X-100. X100. Z-200. Z0.
G00 X150. (OVERTRAVEL ALARM)
G23
G00 X150. (SAFE MOVE)

Enables software-defined movement limits to protect axes during automation.

---

📌 16. Example — Automatic Drill Array with Limit Check

#100 = 0
WHILE [#100 LT 6] DO1
IF [#100 GT 4] GOTO 200
G81 X[#100*20] Y0 Z-20. R2. F150
#100 = [#100 + 1]
END1
N200 M30

Automatically stops drilling when position exceeds limit — combines IF and WHILE logic.

---

📌 17. AI-Driven Macro Trends (2025–2030)

• Self-optimizing macros: AI adjusts cycle count based on tool wear sensors.
• Dynamic limit checking (G22++): Real-time collision prediction.
• Loop learning systems: Adaptive repetition based on load/temperature data.
• Cloud-linked subprograms: Shared machining templates across multiple CNCs.
• Predictive conditional logic: Machines make their own “if” decisions using vibration and torque analytics.

---

✅ Conclusion

By mastering subprograms, loops, and conditional logic, you elevate CNC programming from manual code repetition to smart, modular automation.
G22/G23 protect your hardware, M98/M99 organize your logic, and macros give your CNC the ability to think, adapt, and repeat perfectly — every single time.