Control a NEMA17 Stepper Motor with Arduino UNO & CNC Shield v3.0 Using Assembly

This educational guide teaches you how to control a NEMA17 motor using only Assembly language on an Arduino UNO with the CNC Shield v3.0 — all without Arduino IDE or any libraries.

Why Use Assembly?

Unlike typical tutorials, we go straight to the heart of the ATmega328P microcontroller. No abstractions, just real registers and bits — just like how the datasheet shows. This method helps you truly understand how microcontrollers work at the lowest level.

Pin Mapping Based on Datasheet

Many beginners get confused by multiple names for the same pin:

• Enable: Called D8 or PB0 — in the datasheet, it's Register 4, Bit 0
• Step X: Called D2 or PD2 — in the datasheet, it's Register 9, Bit 2

We ignore symbolic names and use only numeric registers and bits as described in the ATmega328 datasheet.

Assembly Code Example

Paste the following code into costycnc.github.io/avr-compiler-js, compile, and upload to your Arduino UNO:

.org 0
rjmp init
.org 0x60
init:
    sbi 4,0       ; Enable driver (Register 4, Bit 0)
    ldi r18,10    ; Load delay loop counter
    call wait
    sbi 9,2       ; Step pulse X motor (Register 9, Bit 2)
    rjmp init

wait:
    inc r17
    brne wait
    dec r18
    brne wait
    ret

What This Code Does

• Enables the stepper driver by writing 1 to Register 4, Bit 0
• Creates a delay using a simple loop
• Sends a step pulse to Register 9, Bit 2 to turn the motor

Try It Now

1. Connect your Arduino UNO with CNC Shield v3.0
2. Insert a NEMA17 motor in the X slot
3. Go to costycnc.github.io/avr-compiler-js
4. Paste the code and hit UPLOAD after selecting your port
5. Watch your motor turn!

Conclusion

This method teaches students how to interact directly with hardware — no IDEs, no libraries, no abstractions. Just pure control using the ATmega328's datasheet and logic.

🔧 This is real engineering — and you can learn it now.