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Gcode G代码详解(2)

时间:2013-03-05 14:44 来源:未知 作者:中国3d打印网 阅读:
极光尔沃

reprap wiki上面的Gcode说明

G-code
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Contents [hide]
1 Introduction
2 RepRap G Code Fields
3 Comments
4 Individual commands 
4.1 Checking 
4.1.1 N and *
4.2 Buffered G Commands 
4.2.1 G0: Rapid move
4.2.2 G1: Controlled move
4.2.3 G28: Move to Origin
4.3 Unbuffered G commands 
4.3.1 G4: Dwell
4.3.2 G20: Set Units to Inches
4.3.3 G21: Set Units to Millimeters
4.3.4 G90: Set to Absolute Positioning
4.3.5 G91: Set to Relative Positioning
4.3.6 G92: Set Position
4.4 Unbuffered M and T commands 
4.4.1 M0: Stop
4.4.2 M17: Enable/Power all stepper motors
4.4.3 M18: Disable all stepper motors
4.4.4 M20: List SD card
4.4.5 M21: Initialise SD card
4.4.6 M22: Release SD card
4.4.7 M23: Select SD file
4.4.8 M24: Start/resume SD print
4.4.9 M25: Pause SD print
4.4.10 M26: Set SD position
4.4.11 M27: Report SD print status
4.4.12 M28: Begin write to SD card
4.4.13 M29: Stop writing to SD card
4.4.14 M40: Eject
4.4.15 M41: Loop
4.4.16 M42: Stop on material exhausted
4.4.17 M43: Stand by on material exhausted
4.4.18 M80: ATX Power On
4.4.19 M81: ATX Power Off
4.4.20 M84: Stop idle hold
4.4.21 M92: Set axis_steps_per_unit
4.4.22 M101 Turn extruder 1 on Forward
4.4.23 M102 Turn extruder 1 on Reverse
4.4.24 M103 Turn all extruders off
4.4.25 M104: Set Extruder Temperature (Fast)
4.4.26 M105: Get Extruder Temperature
4.4.27 M106: Fan On
4.4.28 M107: Fan Off
4.4.29 M108: Set Extruder Speed
4.4.30 M109: Set Extruder Temperature
4.4.31 M110: Set Current Line Number
4.4.32 M111: Set Debug Level
4.4.33 M112: Emergency Stop
4.4.34 M113: Set Extruder PWM
4.4.35 M114: Get Current Position
4.4.36 M115: Get Firmware Version and Capabilities
4.4.37 M116: Wait
4.4.38 M117: Get Zero Position
4.4.39 M118: Negotiate Features
4.4.40 M119: Get Endstop Status
4.4.41 M126: Open Valve
4.4.42 M127: Close Valve
4.4.43 M128: Extruder Pressure PWM
4.4.44 M129: Extruder pressure off
4.4.45 M140: Bed Temperature (Fast)
4.4.46 M141: Chamber Temperature (Fast)
4.4.47 M142: Holding Pressure
4.4.48 M143: Maximum hot-end temperature
4.4.49 M160: Number of mixed materials
4.4.50 M203: Record Z adjustment
4.4.51 M226: Gcode Initiated Pause
4.4.52 M227: Enable Automatic Reverse and Prime
4.4.53 M228: Disable Automatic Reverse and Prime
4.4.54 M229: Enable Automatic Reverse and Prime
4.4.55 M230: Disable / Enable Wait for Temperature Change
4.4.56 M240: Start conveyor belt motor
4.4.57 M241: Stop conveyor belt motor
4.4.58 M245: Start cooler
4.4.59 M246: Stop cooler
4.4.60 M300: Play beep sound
4.4.61 T: Select Tool
5 Proposed EEPROM configuration codes
6 Replies from the RepRap machine to the host computer
7 Proposal for sending multiple lines of G-code 
7.1 Problem to solve

Introduction 
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. 

TO find out which specific gcode/s are implemented in any given firmware, please see the Firmware_features page. 

(For the technically minded, the end of line is marked by both a <nl> and a <cr>. If you want to manually enter GCodes in your reprap using the Arduino Serial interface, make sure to select "Both NL & CR" on the bottom of the screen.) 

This isn't accurate, firmware accepts single <nl> as well as single <cr>, or combinations thereof. Hosts should accepts all four combinations as well. --Traumflug 09:34, 20 April 2011 (UTC) 

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. 

Letter  Meaning  
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. (Speed of print head movement)  
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. It is common for newer stepper based systems to interpret ... Better: Skeinforge 40 and up interprets this as the absolute length of input filament to consume, rather than the length of the extruded output.  
Nnnn  Line number. Used to request repeat transmission in the case of communications errors.  
*nnn  Checksum. Used to check for communications errors.  
Comments 
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. 

Individual commands 
Checking 
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 
Example: G28 

This causes the RepRap machine to move back to its X, Y and Z zero endstops, a process known as "homing". 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. 

G4: Dwell 
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 
Example: G20 

Units from now on are in inches. 

G21: Set Units to Millimeters 
Example: G21 

Units from now on are in millimeters. (This is the RepRap default.) 

G90: Set to Absolute Positioning 
Example: G90 

All coordinates from now on are absolute relative to the origin of the machine. (This is the RepRap default.) 

G91: Set to Relative Positioning 
Example: G91 

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 
M0: Stop 
Example: M0 

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. 

M17: Enable/Power all stepper motors
Example: M17 

M18: Disable all stepper motors
Example: M18 

Disables stepper motors and allows axis to move 'freely.' 

M20: List SD card 
Example: M20 

All files in the root folder of the SD card are listed to the serial port. This results in a line like: 

ok Files: {SQUARE.G,SQCOM.G,} 

The trailing comma is optional. Note that file names are returned in upper case, but - when sent to the M23 command (below) they must be in lower case. This seems to be a function of the SD software. Go figure... 

M21: Initialise SD card 
Example: M21 

The SD card is initialised. If an SD card is loaded when the machine is switched on, this will happen by default. SD card must be initialised for the other SD functions to work. 

M22: Release SD card 
Example: M22 

SD card is released and can be physically removed. 

M23: Select SD file 
Example: M23 filename.gco 

The file specified as filename.gco (8.3 naming convention is supported) is selected ready for printing. 

M24: Start/resume SD print 
Example: M24 

The machine prints from the file selected with the M23 command. 

M25: Pause SD print 
Example: M25 

The machine pause printing at the current position within the file selected with the M23 command. 

M26: Set SD position 
Example: M26 

Set SD position in bytes (M26 S12345). 

M27: Report SD print status 
Example: M27 

Report SD print status. 

M28: Begin write to SD card 
Example: M28 filename.gco 

File specified by filename.gco is created (or overwritten if it exists) on the SD card and all subsequent commands sent to the machine are written to that file.

M29: Stop writing to SD card 
Example: M29 filename.gco 

File opened by M28 command is closed, and all subsequent commands sent to the machine are executed as normal. 

M40: Eject 
If your RepRap machine can eject the parts it has built off the bed, this command executes the eject cycle. This usually involves cooling the bed and then performing a sequence of movements that remove the printed parts from it. The X, Y and Z position of the machine at the end of this cycle are undefined (though they can be found out using the M114 command, q.v.). 

See also M240 and M241 below. 

M41: Loop 
Example: M41 

If the RepRap machine was building a file from its own memory such as a local SD card (as opposed to a file being transmitted to it from a host computer) this goes back to the beginning of the file and runs it again. So, for example, if your RepRap is capable of ejecting parts from its build bed then you can set it printing in a loop and it will run and run. Use with caution - the only things that will stop it are: 

1.When you press the reset button, 
2.When the build material runs out (if your RepRap is set up to detect this), and 
3.When there's an error (such as a heater failure). 
M42: Stop on material exhausted 
Example: M42 

If your RepRap can detect when its material runs out, this decides the behaviour when that happens. The X and Y axes are zeroed (but not Z), and then the machine shuts all motors and heaters off. You have to press reset to reactivate the machine. In other words, it parks itself and then executes an M0 command (q.v.). 

M43: Stand by on material exhausted 
Example: M43 

If your RepRap can detect when its material runs out, this decides the behaviour when that happens. The X and Y axes are zeroed (but not Z), and then the machine shuts all motors and heaters off except the heated bed, the temperature of which is maintained. The machine will still respond to G and M code commands in this state. 

M80: ATX Power On 
Example: M80 

Turns on the ATX power supply from standby mode to fully operational mode. No-op on electronics without standby mode. 

Note: some firmwares, like Teacup, handle power on/off automatically, so this is redundant there. 

M81: ATX Power Off 
Example: M81 

Turns off the ATX power supply. Counterpart to M80. 

M84: Stop idle hold 
Example: M84 

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. 

M92: Set axis_steps_per_unit 
Example: M92 X<newsteps> Sprinter and Marlin 

Allows programming of steps per unit of axis till the electronics are reset for the specified axis. Very useful for calibration. 

M101 Turn extruder 1 on Forward 
Depreciated. see MCodeReference. Was used by older style DC extruders. See also Bits From Bytes 

M102 Turn extruder 1 on Reverse 
Depreciated. see MCodeReference. Was used by older style DC extruders. See also Bits From Bytes 

M103 Turn all extruders off 
Depreciated. see MCodeReference. Was used by older style DC extruders. See also Bits From Bytes 




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 
Example: M105 

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 
Example: M106 S127 

Turn on the cooling fan at half speed. Optional parameter 'S' declares the PWM value (0-255) 

M107: Fan Off 
Example: M107 

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 
Example: M112 

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 
Example: M113 

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: 

M113 S0.7 

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 
Example: M114 

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 
Example: M115 

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 inconsistently implemented, and should not be relied upon to exist, or output correctly in all cases. 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. 

M116: Wait 
Example: M116 

Wait for all temperatures and other slowly-changing variables to arrive at their set values. See also M109. 

M117: Get Zero Position 
Example: M117 

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.) 

M118: Negotiate Features 
Example: M118 P42 

This M-code is for future proofing. NO firmware or hostware supports this at the moment. It is used in conjunction with M115's FEATURES keyword. 

See Protocol_Feature_Negotiation for more info. 

M119: Get Endstop Status 
Example: M119 

Returns the current state of the configured X,Y,Z endstops. Should take into account any 'inverted endstop' settings, so one can confirm that the machine is interpreting the endstops correctly. 

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. 

M128: Extruder Pressure PWM 
Example: M128 S255 

PWM value to control internal extruder pressure. S255 is full pressure. 

M129: Extruder pressure off 
Example: M129 P100 

In addition to setting Extruder pressure to 0, you can turn the pressure off entirely. P400 will wait 100ms 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. 

M143: Maximum hot-end temperature 
Example: M143 S275 

Set the maximum temperature of the hot-end to 275C 

When temperature of the hot-end exceeds this value, take countermeasures, for instance an emergency stop. This is to prevent hot-end damage. 

M160: Number of mixed materials 
Example: M160 S4 

Set the number of materials, N, that the current extruder can handle to the number specified. The default is 1. 

When N >= 2, then the E field that controls extrusion requires N+1 values separated by spaces after it like this: 

M160 S4
G1 X90.6 Y13.8 E22.4 0.1 0.1 0.1 0.7
G1 X70.6 E42.4 0.0 0.0 0.0 1.0
G1 E42.4 1.0 0.0 0.0 0.0
The second line moves straight to the point (90.6, 13.8) extruding 22.4mm of filament. The mix ratio at the end of the move is 0.1:0.1:0.1:0.7. 

The third line moves back 20mm in X extruding 20mm of filament. The mix varies linearly from 0.1:0.1:0.1:0.7 to 0:0:0:1 as the move is made. 

The fourth line has no physical effect, but sets the mix proportions for the start of the next move to 1:0:0:0. 

M203: Record Z adjustment 
Example: M203 Z-0.75 

This records a Z offset in non-volatile memory in RepRap's microcontroller where it remains active until next set, even when the power is turned off and on again. If the first layer is too close to the bed, you need to effectively move the bed down, so the Z value will be negative. If the nozzle is too far from the bed during the first layer, the Z value should be positive to raise the bed. The maximum adjustment is +/-1.27mm. 

M226: Gcode Initiated Pause 
Example: M226 

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 
Example: M228 

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 




M240: Start conveyor belt motor 
Example: M240 

The conveyor belt allows to start mass production of a part with a reprap 

M241: Stop conveyor belt motor 
Example: M241 




M245: Start cooler 
Example: M245 

used to cool parts/heated-bed down after printing for easy remove of the parts after print 

M246: Stop cooler 
Example: M246 

M300: Play beep sound 
Usage: M300 S<frequency Hz> P<duration ms> 

Example: M300 S300 P1000 

Play beep sound, use to notify important events like the end of printing. See working example on R2C2 electronics. 

T: Select Tool 
Example: T1 

Select extruder number 1 to build with. Extruder numbering starts at 0. 

Proposed EEPROM configuration codes 
BRIEFLY: each RepRap has a number of physical parameters that should be persistent, but easily configurable, such as extrusion steps/mm, various max values, etc. Those parameters are currently hardcoded in the firmware, so that a user has to modify, recompile and re-flash the firmware for any adjustments. These configs can be stored in MCU's EEPROM and modified via some M-codes. Please see the detailed proposal at M-codes for EEPROM config. (This is proposed by --AlexRa on 11-March-2011. There is currently no working implementation of the proposed commands). 

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] 

xx can be one of: 

ok 

rs 

!! 

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. If such temperatures don't exist (for example for an extruder that works at room temperature and doesn't have a sensor) then a value below absolute zero (-273oC) is returned. 

C: means that coordinates follow. Those are the X: Y: etc values. These are only sent in response to M114 and M117. 

The RepRap machine may also send lines that look like this: 

// This is some debugging or other information on a line on its own. It may be sent at any time. 

Such lines will always be preceded by //. 

The most common response is simply: 

ok 

When the machine boots up it sends the string 

start 

once to the host before sending anything else. This should not be replaced or augmented by version numbers and the like. M115 (see above) requests those. 

All this means that every line sent by RepRap to the host computer except the start line has a two-character prefix (one of ok, rs, !! or //). The machine should never send a line without such a prefix. 

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