RJ-11 or RJ-12 to USB adapter, Closed loop hybrid stepper servo, HBS57 driver

Hi,
I'm going to connect a closed loop hybrid stepper servo motor below to a
HBS57 stepper driver.
This will connect to my Arduino Pro Mini.
I wanted to avoid using a level shifter so now I will try to use the 5v vs 3.3v version of the Pro Mini.
The driver says it can accept 5-24V signals.

The issue is I need to connect the driver to a PC with a USB to RS232 connector in order to configure it.
I can't figure out based on the manual if it's an RJ-12 connection or RJ-11.
I'm assuming it's RJ-12, but the manual says NC, NC at the beginning and end connection.
I can't determine if this stands for no wires or something else.

NEMA17 closed loop hybrid servo
The link to their software (in need of translation):
HBS57 software needs english version

This youtube video is the closest thing I could find to help with translation:

rj11 vs rj12.PNG

hbs57 manual connections.PNG

rj11 vs rj12.PNG

hbs57 manual connections.PNG

HBS57 Manual.pdf (221 KB)

I'm assuming it's RJ-12, but the manual says NC, NC at the beginning and end connection.
I can't determine if this stands for no wires or something else.

It usually stands for Not Connected, so that pin is not used. My interpretation is that the inner 4 pins of a RJ12 connector (which equals a RJ11 connector as there the outer two pins are not available) have the UART and power wires. So you can use a RJ11 connector (much easier to get) and connect pin 1 to 5V, pin 2 to the RX, pin 3 to GND and pin 4 to TX (UART are cross connected).