I have FTDI Chip, Null Modem Cable USB - USB NMC-2.5M from “FT232RL”
https://uk.rs-online.com/web/p/interface-development-kits/0537420/
This is my output:
[hEX S | RB760iGS] > /system console print
Flags: X - disabled, U - used, F - free
# PORT TERM
0 serial0 vt102
[hEX S | RB760iGS] > /port print
Flags: I - inactive
# DEVICE NAME CHANNELS USED-BY BAUD-RATE
0 I serial0 1 auto
1 usb2 1 9600
When connected to PC this is dmesg:
[Wed Jun 24 15:03:32 2020] usb 3-1.2: new full-speed USB device number 5 using xhci_hcd
[Wed Jun 24 15:03:32 2020] usb 3-1.2: New USB device found, idVendor=0403, idProduct=6001, bcdDevice= 6.00
[Wed Jun 24 15:03:32 2020] usb 3-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[Wed Jun 24 15:03:32 2020] usb 3-1.2: Product: USB Null Modem Cable
[Wed Jun 24 15:03:32 2020] usb 3-1.2: Manufacturer: FTDI
[Wed Jun 24 15:03:32 2020] usb 3-1.2: SerialNumber: FTBF8HE3
[Wed Jun 24 15:03:32 2020] ftdi_sio 3-1.2:1.0: FTDI USB Serial Device converter detected
[Wed Jun 24 15:03:32 2020] usb 3-1.2: Detected FT232RL
[Wed Jun 24 15:03:32 2020] usb 3-1.2: FTDI USB Serial Device converter now attached to ttyUSB1
But still unable to connect 
I have tried the following, but I get no console.
sudo agetty -L 9600 ttyUSB1 vt102
sudo agetty -L 9600 ttyUSB1 linux
I have added the usb2 port to the console (assuming it is the usb2 as it changed from 0 to 1, when I plugged the cable in)
This is the output on print in system-console:
/system console add port=usb2
[hEX S | RB760iGS] /system console> print
Flags: X - disabled, U - used, F - free
# PORT TERM
0 serial0 vt102
1 X usb2 vt102
And I can not enable it …
What am I doing wrong?