> For the complete documentation index, see [llms.txt](https://docs.smart-stuff.nl/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.smart-stuff.nl/p1-modbus-dongle/firmware-v2-current/led-indicators.md).

# LED indicators

The available LEDs depend on the hardware variant. Firmware v2 uses the status LED for operating state and diagnostics. Separate power and P1 output LEDs, when present, have a fixed hardware function.

| Hardware variant                      | LEDs                                                                                       |
| ------------------------------------- | ------------------------------------------------------------------------------------------ |
| P1 Modbus Pro (regular NRGD)          | Separate blue mono status LED, green mono power LED on the P1 input and mono P1 output LED |
| P1 Modbus Pro (ZAP2/NRGDH-based NRGD) | RGB status LED in the P1 input and mono P1 output LED; no separate blue status LED         |
| D1MC                                  | RGB status LED                                                                             |

The old white P1 Modbus adapter uses mono status and power LEDs. It is legacy hardware and is not part of the current hardware comparison.

## Power LED

On a regular NRGD, the green LED in the P1 input is on when the adapter has power. During normal operation this LED should stay on continuously. On the ZAP2/NRGDH-based NRGD, an RGB status LED occupies this position instead. If the adapter is off or unstable, check the P1 cable, USB power and smart meter power supply.

## P1 output LED

On P1 Modbus Pro, the P1 output LED indicates outgoing P1 data. It blinks when the adapter transmits data on the P1 output. D1MC has no P1 output.

## Status LED

On D1MC and the ZAP2/NRGDH-based NRGD, the RGB status LED color indicates the current state. Both implementations use exactly the same RGB colors and indications shown in the table below. On the regular NRGD, the separate blue mono status LED shows the equivalent state without color.

Firmware v1 does not use the RGB status LED behaviour described here. For v1 installations, the status LED is mono.

| State                               | RGB status LED                               | Mono status LED                          | Meaning                                                                                                 |
| ----------------------------------- | -------------------------------------------- | ---------------------------------------- | ------------------------------------------------------------------------------------------------------- |
| Startup                             | Soft white breathing                         | Soft breathing                           | The dongle is booting. This normally lasts about 3 seconds.                                             |
| Ready                               | Solid blue                                   | On                                       | The dongle is running normally and ready.                                                               |
| Smart meter telegram received       | Short green flash                            | Short blink                              | A valid smart meter telegram has been received successfully.                                            |
| Read, parse or Modbus request error | Red pulse                                    | Two short flashes                        | The dongle detected an error.                                                                           |
| RS485 module missing                | Three short red flashes, followed by a pause | Three short flashes, followed by a pause | The RS485 module is not detected. Modbus communication is disabled until the module is available again. |

## Button feedback

When the button is pressed, hardware with an RGB status LED temporarily shows the button action:

| Button action                          | RGB LED indication                       | Result                               |
| -------------------------------------- | ---------------------------------------- | ------------------------------------ |
| Short press                            | Green while the button is pressed        | Reboot the dongle.                   |
| Press and hold for more than 5 seconds | Green at first, then red after 5 seconds | Restore factory settings and reboot. |