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Marlin [BUG] No connection to MMU2s, only after flashing


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Keine Verbindung von SKR 1.3 zum MMU2s mit Marlin 2.0 (Heute runtergeladen). MMU2s reagiert auf Reset aber mehr nicht. Erst nach dem ich das MMU2s geflasht habe über PrusaSlicer habe ich eine Verbindung und kann per Display es bedienen. Nach einen Rest oder Neustart geht wieder nichts. Erst nach dem erneuten Flashen des MMU2s.


No connection from SKR 1.3 to MMU2s with Marlin 2.0 (downloaded today). MMU2s responds to reset but nothing more. Only after I have flashed the MMU2s on PrusaSlicer I have a connection and can operate it on the display. After a rest or a restart is nothing. Only after re-flashing the MMU2s.

Steps to Reproduce


  1. 3D Drucker Starten.
  2. LED's des MMU2s leuchten auf.
  3. Filament übers Display Laden.
  4. Keine Verbindung zum MMU2s
  5. Flashen des MMU2s
  6. Verbindung zum MMU2s hergestellt.
  7. Filament übers Display laden möglich.
  8. Nach Neustart oder Rest wieder Flashen nötig.


  1. Start 3D printer.
  2. LEDs of the MMU2 light up.
  3. Load filament over the display.
  4. No connection to the MMU2s
  5. Flashing the MMU2s
  6. Connection made to MMU2s.
  7. Loading filament via the display possible.
  8. After restart or rest, flash again.

Additional Information

That's a useful answer
Without any help

@boelle I don't know, It could by a wiring problem or bad configuration in marlin or marlin itself, but I'm running a MMU2 with a SKR PRO and it works well... @Sythx you have to try various things:

I'm starting from scratch:

-You need to connect your MMU to the TFT port:

Capture d’écran 2019-11-03 à 20 27 57 make sure to put the MMU RX wire on the TX pin on the board and the MMU TX wire on the RX pin on the board

You should have (in the order):

-+5V --> BLUE -GND--> NOTHING -TX0 --> WHITE -RX0 --> GREEN -RST --> BROWN (this pin I'm not sure, try it)

Now you need to configure marlin like:

Capture d’écran 2019-11-03 à 20 40 34

Capture d’écran 2019-11-03 à 21 00 16

You must find the right serial port to communicate with the MMU2 according to those available in the HAL.h file (right part of the screenshot). In the exemple above I have Serial1 because in the HAL.h of my CPU I have this port enable. On the screenshot you can see all available ports for your hardware.

I can't do nothing more I don't have this board and I don't know anyone who has it with an MMU2, sorry :(