MMU3 Messages

Starting with the version 2.0.19 of the MMU firmware, requests and responses have a trailing section that contains the CRC8 of the original message. The general structure is as follows:

Requests (what Marlin requests):
MMU3:>{RequestMsgCode}{Value}*{CRC8}\n

Responses (what MMU responds with):
MMU3:<{RequestMsgCode}{Value} {ResponseMsgParamCode}{paramValue}*{CRC8}\n

An example of that would be:

MMU3:>S0*c6\n
MMU3:<S0 A3*22\n

MMU3:>S1*ad\n
MMU3:<S1 A0*34\n

MMU3:>S2*10\n
MMU3:<S2 A2*65\n

This set of responses combines to indicate firmware version 3.0.2.

Startup sequence

When initialized the MMU waits for requests. Marlin repeatedly sends S0 commands until it gets an answer:

MMU3:>S0*c6\n
MMU3:>S0*c6\n
MMU3:>S0*c6\n
...

Once communication is established the MMU responds with:

MMU3:<S0 A3*22\n

Then Marlin continues to get the rest of the MMU firmware version.

MMU3:>S1*ad\n
MMU3:<S1 A0*34\n
MMU3:>S2*10\n
MMU3:<S2 A2*65\n

Setting the stepper mode to SpreadCycle (M0) or StealthChop (M1):

MMU3:>M1*{CRC8};
MMU3:<---nothing---

MMU3:>P0
MMU3:<P0 A{FINDA status}*{CRC8}\n

At this point we can be sure the MMU is available and ready. If there was a timeout or other communication problem somewhere, the printer will not be killed, but for safety the MMU feature will be disabled.

• Firmware version is an integer value, and we care about it. As there is no other way of knowing which protocol to use.
• FINDA status is 1 if the filament is loaded to the extruder, 0 otherwise.

The Firmware version is checked against the required value. If it doesn't match the printer will not be halted, but for safety the MMU feature will be disabled.

Toolchange

MMU3:>T{Filament index}*{CRC8}\n
MMU3:<Q0*ea\n

The MMU sends:

MMU3:<T{filament index}*P{ProgressCode}{CRC8}\n

Which in normal operation would be as follows, let's say that we requested MMU to load `T0``:

MMU3:>T0*{CRC8}\n

MMU3:>Q0*{CRC8}\n
MMU3:<T0*P5{CRC8}\n  # P5 => FeedingToFinda

MMU3:>Q0*{CRC8}\n
MMU3:<T0*P7{CRC8}\n  # P7 => FeedingToNozzle

As soon as the filament is fed down to the extruder we follow with:

MMU3:>C0*{CRC8}\n

The MMU will feed a few more millimeters of filament for the extruder gears to grab. When done, the MMU sends:

MMU3:>Q0*{CRC8}\n
MMU3:<T0*P9{CRC8}\n  # P9 => FinishingMoves

After the T0*P9 response we immediately continue with the next G-code which should be one or more extruder moves to feed the filament into the hotend.

FINDA status

MMU3:>P0*{CRC8}\n

If the filament is loaded to the extruder, FINDA status is 1 and the MMU responds with:

MMU3:<P0 A1*{CRC8}\n

…otherwise it replies:

MMU3:<P0 A0*7b\n

This could be used as a filament runout sensor if polled regularly.

Load filament

To load a filament to the MMU itself, we run:

MMU3:>L{Filament index}*{CRC8}\n
MMU3:<L{Filament index} A1*{CRC8}\n

…and immediately after that we query the status:

MMU3:>Q0*{CRC8}\n

The MMU will respond with status messages:

MMU3:<L0*P5{CRC8}\n

The MMU will load the filament and when done:

MMU3:>Q0*{CRC8}\n
MMU3:<L0*P9{CRC8}\n

Unload filament

• MMU <= 'U0\n'

The MMU will retract current filament from the extruder, and when done:

• MMU => 'ok\n'

Eject filament

• MMU <= 'E*Filament index*\n'
• MMU => 'ok\n'