Documentation on M/GCodes  

Active Member

I'm sorry if this is something covered in a FAQ somewhere but I've been looking around for hours for a more detailed information on the Marlin GCode fork used by Prusa for the MK3S with little progress.  Here's the closest thing that I've found and while it does seem to be authoritative, it is somewhat lacking in details: Prusa-Firmware-Doc

Specifically, I'm trying to sort out whether the G28 command disables mesh bed leveling or not and if it does, how to re-enable it as the Prusa fork doesn't support the M420 command or at least it isn't shown in the referenced document.  Is there a place where the behavior and options for each of the M and G codes specific to my Prusa are described in more detail?

Sincerely appreciate any help offered.


Posted : 07/01/2020 6:42 pm
Noble Member

This is my source of the prusa specific implementation:

Often linked posts:
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Posted : 07/01/2020 11:29 pm
Active Member


Hi and thank you!  

I've looked through the repo and here's what I "think" I've sorted out but wanted to confirm with you:

If != zero before the G28 was processed and only X and Y axis are homed, the mbl will be reactivated and the z axis will be appropriately compensated based on it just at the end of completing G28.  However, for this to be true, MESH_BED_LEVELING must be defined.  The problem I'm having is that I can't figure out where that happens. 

I'm sorry for asking a lame coding question as I think I can just accept on faith that it gets defined somewhere and I have my answer about the behavior of G28 for my situation but I'm bummed out that I can't figure out where the #define is.  If it's any consolation, if I know this, it may eliminate future questions!




Posted : 08/01/2020 3:19 am

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