- 1 Introduction
- 2 RepRap G Code Fields
- 3 Comments
- 4 Individual commands
- 4.1 Checking
- 4.2 Buffered G Commands
- 4.3 Unbuffered G commands
- 4.4 Unbuffered M and T commands
- 4.4.1 M0: Stop
- 4.4.2 M84: Stop idle hold
- 4.4.3 M104: Set Extruder Temperature (Fast)
- 4.4.4 M105: Get Extruder Temperature
- 4.4.5 M106: Fan On
- 4.4.6 M107: Fan Off
- 4.4.7 M108: Set Extruder Speed
- 4.4.8 M109: Set Extruder Temperature
- 4.4.9 M110: Set Current Line Number
- 4.4.10 M111: Set Debug Level
- 4.4.11 M112: Emergency Stop
- 4.4.12 M113: Set Extruder PWM
- 4.4.13 M114: Get Current Position
- 4.4.14 M115: Get Firmware Version and Capabilities
- 4.4.15 M116: Wait
- 4.4.16 M117: Get Zero Position
- 4.4.17 M126: Open Valve
- 4.4.18 M127: Close Valve
- 4.4.19 M140: Bed Temperature (Fast)
- 4.4.20 M141: Chamber Temperature (Fast)
- 4.4.21 M142: Holding Pressure
- 4.4.22 M226: Gcode Initiated Pause
- 4.4.23 M227: Enable Automatic Reverse and Prime
- 4.4.24 M228: Disable Automatic Reverse and Prime
- 4.4.25 M229: Enable Automatic Reverse and Prime
- 4.4.26 M230: Disable / Enable Wait for Temperature Change
- 4.4.27 T: Select Tool
- 4.5 RepRap G-Code Summary Table
- 5 Replies from the RepRap machine to the host computer
This page describes the G Codes that the RepRap firmware uses and how they work.
The list of what can be done is extensible. But check this page first, and add your extension here first before you implement it.
A typical piece of GCode as sent to a RepRap machine might look like this:
N3 T0*57 N4 G92 E0*67 N5 G28*22 N6 G1 F1500.0*82 N7 G1 X2.0 Y2.0 F3000.0*85 N8 G1 X3.0 Y3.0*33
The meaning of all those symbols and numbers (and more) is explained below.
RepRap G Code Fields
This section explains the letter-preceded fields. The numbers in the fields are represented by nnn. Numbers can be integers, or can contain a decimal point, depending on context. For example an X coordinate can be integer (X175) or fractional (X17.62), whereas trying to select extruder number 2.76 would make no sense.
|Gnnn||Standard GCode command, such as move to a point|
|Mnnn||RepRap-defined command, such as turn on a cooling fan|
|Tnnn||Select tool nnn. In RepRap, tools are extruders|
|Snnn||Command parameter, such as the voltage to send to a motor|
|Pnnn||Command parameter, such as a time in milliseconds|
|Xnnn||An X coordinate, usually to move to|
|Ynnn||A Y coordinate, usually to move to|
|Znnn||A Z coordinate, usually to move to|
|Innn||Parameter - not currently used|
|Jnnn||Parameter - not currently used|
|Fnnn||Feedrate in mm per minute.|
|Rnnn||Parameter - not currently used|
|Qnnn||Parameter - not currently used|
|Ennn||Length of extrudate in mm. This is exactly like X, Y and Z, but for the length of filament to extrude.|
|Nnnn||Line number. Used to request repeat transmission in the case of communications errors.|
|*nnn||Checksum. Used to check for communications errors.|
G Code comments:
N3 T0*57 ;This is a comment N4 G92 E0*67 ; So is this N5 G28*22
Will be ignored by RepRap, as will blank lines. But it's better to strip these out in the host computer before the lines are sent. This saves bandwidth.
N and *
Example: N123 [...G Code in here...] *71
These are the line number and the checksum. The RepRap firmware checks the checksum against a locally-computed value and, if they differ, requests a repeat transmission of the line of the given number.
You can leave both of these out - RepRap will still work, but it won't do checking. You have to have both or neither though.
The checksum "cs" for a GCode string "cmd" (including its line number) is computed by exor-ing the bytes in the string up to and not including the * character as follows:
int cs = 0; for(i = 0; cmd[i] != '*' && cmd[i] != NULL; i++) cs = cs ^ cmd[i]; cs &= 0xff; // Defensive programming...
and the value is appended as a decimal integer to the command after the * character.
The RepRap firmware expects line numbers to increase by 1 each line, and if that doesn't happen it is flagged as an error. But you can reset the count using M110 (see below).
Buffered G Commands
The RepRap firmware stores these commands in a ring buffer internally for execution. This means that there is no (appreciable) delay while a command is acknowledged and the next transmitted. In turn, this means that sequences of line segments can be plotted without a dwell between one and the next. As soon as one of these buffered commands is received it is acknowledged and stored locally. If the local buffer is full, then the acknowledgment is delayed until space for storage in the buffer is available. This is how flow control is achieved.
G0: Rapid move
Example: G0 X12
In this case move rapidly to X = 12 mm. In fact, the RepRap firmware uses exactly the same code for rapid as it uses for controlled moves (see G1 below), as - for the RepRap machine - this is just as efficient as not doing so. (The distinction comes from some old machine tools that used to move faster if the axes were not driven in a straight line. For them G0 allowed any movement in space to get to the destination as fast as possible.)
G1: Controlled move
Example: G1 X90.6 Y13.8 E22.4
Go in a straight line from the current (X, Y) point to the point (90.6, 13.8), extruding material as the move happens from the current extruded length to a length of 22.4 mm.
RepRap does subtle things with feedrates. Thus:
G1 F1500 G1 X90.6 Y13.8 E22.4
Will set a feedrate of 1500 mm/minute, then do the move described above at that feedrate. But
G1 F1500 G1 X90.6 Y13.8 E22.4 F3000
Will set a feedrate of 1500 mm/minute, then do the move described above accelerating to a feedrate of 3000 mm/minute as it does so. The extrusion will accelerate along with the X, Y movement so everything stays synchronized.
RepRap thus treats feedrate as simply another variable (like X, Y, Z, and E) to be linearly interpolated. This gives complete control over accelerations and decelerations in a way that ensures that everything moves together and the right volume of material is extruded at all points.
The first example shows how to get a constant-speed movement. The second how to accelerate or decelerate. Thus
G1 F1500 G1 X90.6 Y13.8 E22.4 F3000 G1 X80 Y20 E36 F1500
Will do the first movement accelerating as before, and the second decelerating from 3000 mm/minute back to 1500 mm/minute.
To reverse the extruder by a given amount (for example to reduce its internal pressure while it does an in-air movement so that it doesn't dribble) simply use G1 to send an E value that is less than the currently extruded length.
G28: Move to Origin
This causes the RepRap machine to move back to its X, Y and Z zero endstops. It does so accelerating, so as to get there fast. But when it arrives it backs off by 1 mm in each direction slowly, then moves back slowly to the stop. This ensures more accurate positioning.
If you add coordinates, then just the axes with coordinates specified will be zeroed. Thus
G28 X0 Y72.3
will zero the X and Y axes, but not Z. The actual coordinate values are ignored.
Unbuffered G commands
The following commands are not buffered. When one is received it is stored, but it is not acknowledged to the host until the buffer is exhausted and then the command has been executed. Thus the host will pause at one of these commands until it has been done. Short pauses between these commands and any that might follow them do not affect the performance of the machine.
Example: G4 P200
In this case sit still doing nothing for 200 milliseconds. During delays the state of the machine (for example the temperatures of its extruders) will still be preserved and controlled.
G20: Set Units to Inches
Units from now on are in inches.
G21: Set Units to Millimeters
Units from now on are in millimeters. (This is the RepRap default.)
G90: Set to Absolute Positioning
All coordinates from now on are absolute relative to the origin of the machine. (This is the RepRap default.)
G91: Set to Relative Positioning
All coordinates from now on are relative to the last position.
G92: Set Position
Example: G92 X10 E90
Allows programming of absolute zero point, by reseting the current position to the values specified. This would set the machine's X coordinate to 10, and the extrude coordinate to 90. No physical motion will occur.
Unbuffered M and T commands
The RepRap machine finishes any moves left in its buffer, then shuts down. All motors and heaters are turned off. It can be started again by pressing the reset button on the master microcontroller. See also M112.
M84: Stop idle hold
Stop the idle hold on all axis and extruder. In some cases the idle hold causes annoying noises, which can be stopped by disabling the hold. Be aware that by disabling idle hold during printing, you will get quality issues. This is recommended only in between or after printjobs.
M104: Set Extruder Temperature (Fast)
Example: M104 S190
Set the temperature of the current extruder to 190oC and return control to the host immediately (i.e. before that temperature has been reached by the extruder). See also M109.
M105: Get Extruder Temperature
Request the temperature of the current extruder and the build base in degrees Celsius. The temperatures are returned to the host computer. For example, the line sent to the host in response to this command looks like
ok T:201 B:117
M106: Fan On
Turn on the cooling fan (if any).
M107: Fan Off
Turn off the cooling fan (if any).
M108: Set Extruder Speed
Sets speed of extruder motor. (Deprecated in current firmware, see M113)
M109: Set Extruder Temperature
Example: M109 S190
Set the temperature of the current extruder to 190oC and wait for it to reach that value before sending an acknowledgment to the host. In fact the RepRap firmware waits a while after the temperature has been reached for the extruder to stabilise - typically about 40 seconds. This can be changed by a parameter in the firmware configuration file when the firmware is compiled. See also M104 and M116.
M110: Set Current Line Number
Example: N123 M110
Set the current line number to 123. Thus the expected next line after this command will be 124.
M111: Set Debug Level
Example: M111 S6
Set the level of debugging information transmitted back to the host to level 6. The level is the OR of three bits:
#define DEBUG_ECHO (1<<0) #define DEBUG_INFO (1<<1) #define DEBUG_ERRORS (1<<2)
Thus 6 means send information and errors, but don't echo commands. (This is the RepRap default.)
M112: Emergency Stop
Any moves in progress are immediately terminated, then RepRap shuts down. All motors and heaters are turned off. It can be started again by pressing the reset button on the master microcontroller. See also M0.
M113: Set Extruder PWM
Set the PWM for the currently-selected extruder. On its own this command sets RepRap to use the on-board potentiometer on the extruder controller board to set the PWM for the currently-selected extruder's stepper power. With an S field:
it causes the PWM to be set to the S value (70% in this instance). M113 S0 turns the extruder off, until an M113 command other than M113 S0 is sent.
M114: Get Current Position
This causes the RepRap machine to report its current X, Y, Z and E coordinates to the host.
For example, the machine returns a string such as:
ok C: X:0.00 Y:0.00 Z:0.00 E:0.00
M115: Get Firmware Version and Capabilities
Request the Firmware Version and Capabilities of the current microcontroller The details are returned to the host computer as key:value pairs separated by spaces and terminated with a linefeed.
sample data from firmware:
ok PROTOCOL_VERSION:0.1 FIRMWARE_NAME:FiveD FIRMWARE_URL:http%3A//reprap.org MACHINE_TYPE:Mendel EXTRUDER_COUNT:1
This M115 code is NOT yet implemented in any released firmware, and should not be relied upon. An initial implementation was committed to svn for the FiveD Reprap firmware on 11 Oct 2010. Work to more formally define protocol versions is currently (October 2010) being discussed. See M115_Keywords for one draft set of keywords and their meanings.
Wait for all temperatures and other slowly-changing variables to arrive at their set values. See also M109.
M117: Get Zero Position
This causes the RepRap machine to report the X, Y, Z and E coordinates in steps not mm to the host that it found when it last hit the zero stops for those axes. That is to say, when you zero X, the x coordinate of the machine when it hits the X endstop is recorded. This value should be 0, of course. But if the machine has drifted (for example by dropping steps) then it won't be. This command allows you to measure and to diagnose such problems. (E is included for completeness. It doesn't normally have an endstop.)
M126: Open Valve
Example: M126 P500
Open the extruder's valve (if it has one) and wait 500 milliseconds for it to do so.
M127: Close Valve
Example: M127 P400
Close the extruder's valve (if it has one) and wait 400 milliseconds for it to do so.
M140: Bed Temperature (Fast)
Example: M140 S55
Set the temperature of the build bed to 55oC and return control to the host immediately (i.e. before that temperature has been reached by the bed).
M141: Chamber Temperature (Fast)
Example: M141 S30
Set the temperature of the chamber to 30oC and return control to the host immediately (i.e. before that temperature has been reached by the chamber).
M142: Holding Pressure
Example: M142 S1
Set the holding pressure of the bed to 1 bar.
The holding pressure is in bar. For hardware which only has on/off holding, when the holding pressure is zero, turn off holding, when the holding pressure is greater than zero, turn on holding.
M226: Gcode Initiated Pause
Initiates a pause in the same way as if the pause button is pressed.
M227: Enable Automatic Reverse and Prime
Example: M227 P1600 S1600
P and S are steps.
M228: Disable Automatic Reverse and Prime
M229: Enable Automatic Reverse and Prime
Example: M229 P1.0 S1.0
P and S are extruder screw rotations.
M230: Disable / Enable Wait for Temperature Change
Example: M230 S1
S1 Disable wait for temperature change S0 Enable wait for temperature change
T: Select Tool
Select extruder number 1 to build with. Extruder numbering starts at 0.
RepRap G-Code Summary Table
|G0||G||Y||Xnnn Ynnn Znnn Ennn Fnnn||Rapid move to position specified by parameters|
|G1||G||Y||Xnnn Ynnn Znnn Ennn Fnnn||Controlled move to position specified by parameters|
|G4||G||N||Pnnn||Delay for a period of nnn milliseconds|
|G20||G||N||none||Set distance units for motion and position values to inches|
|G21||G||N||none||Set distance units for motion and position values to millimeters (default)|
|G28||G||Y||Xnnn Ynnn Znnn||Move to origin (on specified axes only, if X/Y/Z parameters are present)|
|G90||G||N||none||Set absolute positioning (for subsequent motion commands) (default)|
|G91||G||N||none||Set relative positioning (for subsequent motion commands)|
|G92||G||N||Xnnn Ynnn Znnn Ennn||Define current absolute position|
|M0||M||N||none||Stop (after completing any buffered commands)|
|M104||M||N||Snnn||Set current extruder temperature (in Celsius) to value of parameter, and return|
|M105||M||N||none||Request current extruder and base temperatures (in Celsius)|
|M106||M||N||none||Set cooling fan off|
|M107||M||N||none||Set cooling fan on|
|M108||M||N||Snnn||Set extruder motor speed (DEPRECATED)|
|M109||M||N||Snnn||Set extruder temperature (in Celsius), and wait for it|
|M110||M||N||none||Set current line number to Nxxx value preceeding command|
|M111||M||N||Snnn||Set debug level bitfield to value of parameter (default 6)|
|M112||M||N||none||Emergency stop (stop immediately, discarding any buffered commands)|
|M113||M||N||Snnn||Set Extruder PWM (to value defined by pot, or to parameter value if present)|
|M114||M||N||none||Get Current Position (return current X, Y, Z and E values)|
|M115||M||N||none||Get firmware version (to be implemented)|
|M116||M||N||none||Wait for all temperature and slow-changing variables to reach set values|
|M117||M||N||none||Get Zero Position (return X, Y, Z and E values of endstop hits)|
|M126||M||N||Pnnn||Open Valve and wait for nnn milliseconds for it to open|
|M127||M||N||Pnnn||Close Valve and wait for nnn milliseconds for it to close|
|M140||M||N||Snnn||Set build bed temperature (in Celsius) to value of parameter, and return|
|M141||M||N||Snnn||Set chamber temperature (in Celsius) to value of parameter, and return|
|M142||M||N||Snnn||Set holding pressure of bed to value of parameter|
|M226||M||N||none||Gcode initiated pause|
|M227||M||N||Pnnn Snnn||Enable Automatic Reverse and Prime (steps parameters)|
|M228||M||N||none||Disable Automatic Reverse and Prime|
|M229||M||N||Pnnn Snnn||Enable Automatic Reverse and Prime (rotations parameters)|
|M230||M||N||Sn||Disable / Enable Wait for Temperature Change|
|Tn||T||N||none||Select Tool n (T0 selects tool 0) (default extruder is 0)|
Replies from the RepRap machine to the host computer
All communication is in printable ASCII characters. Messages sent back to the host computer are terminated by a newline and look like this:
xx [line number to resend] [T:93.2 B:22.9] [C: X:9.2 Y:125.4 Z:3.7 E:1902.5] [Some debugging or other information may be here]
where xx can be one of:
ok means that no error has been detected.
rs means resend, and is followed by the line number to resend.
!! means that a hardware fault has been detected. The RepRap machine will shut down immediately after it has sent this message.
The T: and B: values are the temperature of the currently-selected extruder and the bed respectively, and are only sent in response to M105.
C: means that coordinates follow. Those are the X: Y: etc values. These are only sent in response to M114 and M117.
The most common response is simply:
When the machine boots up it sends the string
once to the host before sending anything else. This should not be replaced or augmented by version numbers and the like. We should implement an M code to request those.