Starting from firmware 3.0.0, the Original Prusa Multi-material upgrade (MMU) has a set of runtime variables called registers. You can use these to read or write values into the MMU via G-codes. This article provides the list of available registers in the current firmware.

They can be different error codes and status information related to the MMU (e.g. filament errors, motor errors, temperature warnings, etc), specific parameters (feed rate, acceleration, current, etc), and different components (pulley, selector, idler, etc).

This replaces the Service menu from previous firmware versions.

The table below includes 8-bit (empty value: 0xFFh 255) and 16-bit registers (empty value: 0xFFFFh 65535). The empty values show the maximum amount the register can hold.

There are three different access types:

Read: the register can be only read.
Write: the register can be read and written to. The written change is not persistent (applies only until the reset of the MMU).
Write Persistent: the register can be read and written to. The written values are stored in EEPROM even after the MMU is restarted.

G-codes

Generally, the registers are in the MMU. One of the ways of reading/writing into the registers is through G-codes. The ones you will need here are:

M707: Used to read values from specific addresses (e.g., the version, current error codes, filament state).
M708: Used to write values to specific addresses, allowing for changes in various printer parameters.

Use a program like Putty or Arduino IDE. Using Pronterface might cause damage to your MMU.

Address	Bit/Type	Name	Valid values	Default	Description	Read / Write	Gcode Read	Gcode Write
0x00h 00	uint8	project_major	00h 0	ffh 255	Project Major Version	Read only	M707 A0x00	N/A
0x01h 01	uint8	project_minor	00h 0	ffh 255	Project Minor Version	Read only	M707 A0x01	N/A
0x02h 02	uint8	project_revision	00h 0	ffh 255	Project Revision	Read only	M707 A0x02	N/A
0x03h 03	uint8	project_build _number	00h 0	ffh 255	Project Build Number	Read only	M707 A0x03	N/A
0x04h 04	uint16	MMU_errors	0000h 0	ffffh 65535	MMU Errors	Read / Write Persistent	M707 A0x04	M708 A0x04 Xnnnn
0x05h 05	uint8	Current_Progress_Code	ffh 255	ffh 255	Emtpy	Read only	M707 A0x05	N/A
			00h 0		OK
			01h 1		EngagingIdler
			02h 2		DisengagingIdler
			03h 3		UnloadingToFinda
			04h 4		UnloadingToPulley
			05h 5		FeedingToFinda
			06h 6		FeedingToBondtech
			07h 7		FeedingToNozzle
			08h 8		AvoidingGrind
			09h 9		FinishingMoves
			0ah 10		ERRDisengagingIdler
			0bh 11		ERREngagingIdler
			0ch 12		ERRWaitingForUser
			0dh 13		ERRInternal
			0eh 14		ERRHelpingFilament
			0fh 15		ERRTMCFailed
			10h 16		UnloadingFilament
			11h 17		LoadingFilament
			11h 18		SelectingFilamentSlot
			12h 19		PreparingBlade
			13h 20		PushingFilament
			14h 21		PerformingCut
			15h 22		ReturningSelector
			16h 23		ParkingSelector
			17h 24		EjectingFilament
			18h 25		RetractingFromFinda
			19h 26		Homing
			1ah 27		MovingSelector
			1bh 28		FeedingToFSensor
0x06h 06	uint16	Current_Error_Code	0000h 0	ffffh 65535	RUNNING	Read only	M707 A0x06	N/A
			0001h 1		OK
			8001h 32769		FSENSOR_DIDNT _SWITCH_ON
			8002h 32770		FINDA_DIDNT _SWITCH_OFF
			8003h 32771		FSENSOR_DIDNT _SWITCH_ON
			8004h 32772		FSENSOR_DIDNT _SWITCH_OFF
			8005h 32773		FILAMENT_ALREADY _LOADED
			8006h 32774		INVALID_TOOL
			8007h 32775		Homing_FAILED
			8008h 32776		FINDA_VS_EEPROM _DISREPANCY
			8009h 32777		FSENSOR_TOO _EARLY
			802bh 32811		QUEUE_FULL
			802ch 32812		VERSION_MISMATCH
			802dh 32813		PROTOCOL_ERROR
			802eh 32814		MMU_NOT_RESPONDING
			802fh 32815		INTERNAL
			8200h 33280		TMC_IOIN_MISMATCH
			8240h 33344		TMC_IOIN_MISMATCH PULLEY
			8280h 33408		TMC_IOIN_MISMATCH SELECTOR
			8300h 33536		TMC_IOIN_MISMATCH IDLER
			83C0h 33728		TMC_IOIN_MISMATCH All 3
			8400h 33792		TMC_RESET
			8440h 33856		TMC_RESET PULLEY
			8480h 33920		TMC_RESET SELECTOR
			8500h 34048		TMC_RESET IDLER
			85C0h 34240		TMC_RESET All 3
			8800h 34816		TMC_UNDERVOLTAGE_ON _CHARGE_PUMP
			8840h 34880		TMC_UNDERVOLTAGE_ON _CHARGE_PUMP PULLEY
			8880h 34944		TMC_UNDERVOLTAGE_ON _CHARGE_PUMP SELECTOR
			8900h 35072		TMC_UNDERVOLTAGE_ON _CHARGE_PUMP IDLER
			89C0h 35264		TMC_UNDERVOLTAGE_ON _CHARGE_PUMP All 3
			9000h 36864		TMC_SHORT_TO_GROUND
			9040h 36928		TMC_SHORT_TO_GROUND PULLEY
			9080h 36992		TMC_SHORT_TO_GROUND SELECTOR
			9100h 37120		TMC_SHORT_TO_GROUND IDLER
			91C0h 37312		TMC_SHORT_TO_GROUND All 3
			A000h 40960		TMC_OVER_TEMPERATURE _WARN
			A040h 41024		TMC_OVER_TEMPERATURE _WARN PULLEY
			A080h 41088		TMC_OVER_TEMPERATURE _WARN SELECTOR
			A100h 41216		TMC_OVER_TEMPERATURE _WARN IDLER
			A1C0h 41408		TMC_OVER_TEMPERATURE _WARN All 3
			C000h 49152		TMC_OVER_TEMPERATURE _ERROR
			C040h 49216		TMC_OVER_TEMPERATURE _ERROR PULLEY
			C080h 49280		TMC_OVER_TEMPERATURE _ERROR SELECTOR
			C100h 49408		TMC_OVER_TEMPERATURE _ERROR IDLER
			C1C0h 49600		TMC_OVER_TEMPERATURE _ERROR All 3
0x07h 07	uint8	Filament_State	00h 0	ffh 255	Filament State	Read / Write	M707 A0x07	M708 A0x07 Xnn
0x08h 08	uint8	FINDA_State	00h 0	ffh 255	not triggered	Read only	M707 A0x08	N/A
0x08h 08	uint8	FINDA_State	01h 1	ffh 255	triggered	Read only	M707 A0x08	N/A
0x09h 09	uint8	FSensor_State	00h 0	ffh 255	not triggered	Read / Write	M707 A0x09	M708 A0x09 Xnn
0x09h 09	uint8	FSensor_State	01h 1	ffh 255	triggered	Read / Write	M707 A0x09	M708 A0x09 Xnn
0x0ah 10	uint8	Motor_Mode	00h 0	00h 0	normal	Read only	M707 A0x0a	N/A
0x0ah 10	uint8	Motor_Mode	01h 1	00h 0	stealth	Read only	M707 A0x0a	N/A
0x0bh 11	uint8	extra_load_distance	00h 0	1eh 30	unit mm	Read / Write	M707 A0x0b	M708 A0x0b Xnn
0x0ch 12	uint8	FSensor_unload _check_dist.	00h 0	28h 30	unit mm	Read / Write	M707 A0x0c	M708 A0x0c Xnn
0x0dh 13	uint16	Pulley_unload _feedrate	0000h 0	0078h 120	unit mm/s	Read / Write	M707 A0x0d	M708 A0x0d Xnnnn
0x0eh 14	uint16	Pulley_acceleration	0000h 0	320h 800.0	unit mm/s²	Read (Write)	M707 A0x0e	(M708 A0x0e Xnnnn)
0x0fh 15	uint16	Selector_acceleration	0000h 0	00c8h 200.0	unit mm/s²	Read (Write)	M707 A0x0f	(M708 A0x0f Xnnnn)
0x10h 16	uint16	Idler_acceleration	0000h 0	01f4h 500.0	unit deg/s²	Read (Write)	M707 A0x10	(M708 A0x10 Xnnnn)
0x11h 17	uint16	Pulley_load_feedrate	0000h 0	0050h 80	unit mm/s	Read / Write	M707 A0x11	M708 A0x11 Xnnnn
0x12h 18	uint16	Selector_nominal _feedrate	0000h 0	002dh 45	unit mm/s	Read / Write	M707 A0x12	M708 A0x12 Xnnnn
0x13h 19	uint16	Idler_nominal _feedrate	0000h 0	012ch 300	unit deg/s	Read / Write	M707 A0x13	M708 A0x13 Xnnnn
0x14h 20	uint16	Pulley_slow_feedrate	0000h 0	0014h 20	unit mm/s	Read / Write	M707 A0x14	M708 A0x14 Xnnnn
0x15h 21	uint16	Selector_homing _feedrate	0000h 0	001eh 30	unit mm/s	Read (Write)	M707 A0x15	(M708 A0x15 Xnnnn)
0x16h 22	uint16	Idler_homing _feedrate	0000h 0	0109h 265	unit deg/s	Read (Write)	M707 A0x16	(M708 A0x16 Xnnnn)
0x17h 23	uint8	Pulley_sg_thrs__R	00h 0	08h 8		Read / Write Persistent	M707 A0x17	M708 A0x17 Xnn
0x18h 24	uint8	Selector_sg_thrs_R	00h 0	03h 3		Read / Write Persistent	M707 A0x18	M708 A0x18 Xnn
0x19h 25	uint8	Idler_sg_thrs_R	00h 0	06h 6		Read / Write Persistent	M707 A0x19	M708 A0x19 Xnn
0x1ah 26	uint16	Get Pulley position	0000h 0	ffffh 65535	unit mm	Read only	M707 A0x1a	N/A
0x1bh 27	uint16	Set/Get_Selector_slot	0000h 0	ffffh 65535	unit slot [0-4/5] 5=park pos	Read / Write	M707 A0x1b	M708 A0x1b Xn
0x1ch 28	uint16	Set/Get_Idler_slot	0000h 0	ffffh 65535	unit slot [0-4/5] 5=disengaged	Read / Write	M707 A0x1c	M708 A0x1c Xn
0x1dh 29	uint8	Set/Get Selector cut iRun current	0 to 63 (aka 0-1024mA)	31 (530mA)		Read / Write	M707 A0x1d	M708 A0x1d Xn
0x1eh 30	uint16	Set/Get Pulley iRun current	0-31	14h 20	20->350mA: see TMC2130 current conversion	Read / Write	M707 A0x1e	M708 A0x1e Xn
0x1fh 31	uint16	Set/Get Selector iRun current	0-31	1fh 31	31->530mA: see TMC2130 current conversion	Read / Write	M707 A0x1f	M708 A0x1f Xn
0x20h 32	uint16	Set/Get Idler iRun current	0-31	1fh 31	31->530mA: see TMC2130 current conversion	Read / Write	M707 A0x20	M708 A0x20 Xn
0x21h 33	uint16	Reserved for internal use	225		N/A	N/A	N/A	N/A
0x22h 34	uint16	Bowden length	341-1000	168h 360	unit mm	Read / Write Persistent	M707 A0x22	M708 A0x22 Xn
0x23h 35	uint8	Cut length	0-255	8	unit mm	/ Write \| M	M708 A0x23 \| M	M708 A0x23 Xn

Printer description

Registers MMU (MMU3)