IEC bus and IDE-HD occupy so many pins of the microcontroller that only two pins are left for the user interface. Two LEDs and three buttons are connected to these two pins. The fourth button is the reset button.

There are three LEDs. The left, yellow LED is the activity LED of the HD. The middle, green LED is the NLQHD Activity LED. The right, red LED is the NLQHD error LED.

The left button has no function at the moment. The middle button determines the mode, the right button executes it.
There are modes 1 to 9. The current mode is indicated by the flash number of the green LED. That is, if the green LED flashes 8 times, then the mode 8 is set. If you press the right button now, mode 8 is executed. Currently, there are only two modes that do something:

1 (not yet implemented)
2 (not yet implemented)
3 exits the selection menu
4 (not yet implemented)
5 (not yet implemented)
6 (not yet implemented)
7 exits the selection menu
8 Device swap with drive 8
9 Device swap with drive 9

Here is an example: You have a 1541 with device number 8 and a NLQ-HD with 12. Now press the middle button 8 times, so that the green LED flashes 8 times. Then press the right button. After that the 1541 has the device number 12 and the NLQ-HD 8.

In addition, the buttons are for switching off NLQ-HD: If the right button is held down for a long time (4 seconds), NLQ-HD switches off. The HD is sent to sleep mode and NLQ-HD behaves as if it were not connected to the IEC bus. So 1541 software floppy speaders, with only one single 1541 can be connected, also work. Pressing the center button will awake NLQ-HD.