Overview of G-Code Programming

The LinuxCNC G-code language is based on the RS274/NGC language. The G-code language is based on lines of code. Each line (also called a block) may include commands to do several different things. Lines of code may be collected in a file to make a program.

A typical line of code consists of an optional line number at the beginning followed by one or more words. A word consists of a letter followed by a number (or something that evaluates to a number). A word may either give a command or provide an argument to a command. For example, G1 X3 is a valid line of code with two words. G1 is a command meaning move in a straight line at the programmed feed rate to the programmed end point, and X3 provides an argument value (the value of X should be 3 at the end of the move). Most LinuxCNC G-code commands start with either G or M (for General and Miscellaneous). The words for these commands are called G-codes and M-codes. Also common are subroutine codes that begin with o- which are called o-codes.

El lenguaje LinuxCNC no tiene indicador para el inicio de un programa. El intérprete, sin embargo, se ocupa de los archivos. Un solo programa puede estar en un archivo único, o un programa puede extenderse a través de varios archivos. Un archivo se puede demarcar con porcentajes de la siguiente manera. La primera linea no en blanco de un archivo puede contener solo un signo de porcentaje, %, posiblemente rodeado de espacios en blanco y luego (normalmente al final del archivo) puede haber una línea similar. Demarcar un archivo con porcentajes es opcional si el archivo tiene un M2 o M30, pero es requerido si no los tiene. Se notificará un error si un archivo tiene una línea de porcentaje al principio pero no al final. El contenido util de un archivo delimitado por porcentajes termina después de la segunda línea porcentaje. Cualquier cosa después de eso, se ignora.

The LinuxCNC G-code language has two commands (M2 or M30), either of which ends a program. A program may end before the end of a file. Lines of a file that occur after the end of a program are not to be executed. The interpreter does not even read them.

Una línea permitida de código de entrada consiste en lo siguiente, en orden, con la restricción de que hay un máximo (actualmente 256) al número de caracteres permitidos en una línea.

Any input not explicitly allowed is illegal and will cause the Interpreter to signal an error.

Spaces and tabs are allowed anywhere on a line of code and do not change the meaning of the line, except inside comments. This makes some strange-looking input legal. The line G0X +0. 12 34Y 7 is equivalent to G0 x+0.1234 Y7, for example.

Blank lines are allowed in the input. They are to be ignored.

La entrada no distingue entre mayúsculas y minúsculas, excepto en los comentarios, es decir, cualquier letra fuera de un comentario puede estar en mayúsculas o minúsculas sin cambiar el significado de una línea.

The following rules are used for (explicit) numbers. In these rules a digit is a single character between 0 and 9.

Observe que los ceros inicial (antes del punto decimal y el primer dígito distinto de cero) y final (después del punto decimal y el último dígito distinto de cero) están permitidos pero no son obligatorios. Un número escrito con los ceros iniciales o finales tendrán el mismo valor cuando se lea como si los ceros adicionales no estuvieran allí.

Numbers used for specific purposes in RS274/NGC are often restricted to some finite set of values or some to some range of values. In many uses, decimal numbers must be close to integers; this includes the values of indices (for parameters and carousel slot numbers, for example), M-codes, and G-codes multiplied by ten. A decimal number which is intended to represent an integer is considered close enough if it is within 0.0001 of an integer value.

The RS274/NGC language supports parameters - what in other programming languages would be called variables. There are several types of parameter of different purpose and appearance, each described in the following sections. The only value type supported by parameters is floating-point; there are no string, boolean or integer types in G-code like in other programming languages. However, logic expressions can be formulated with boolean operators ( AND, OR, XOR, and the comparison operators EQ,NE,GT,GE,LT,LE), and the MOD, ROUND, FUP and FIX operators support integer arithmetic.

Parameters differ in syntax, scope, behavior when not yet initialized, mode, persistence and intended use.

If enabled in the INI file G-code has access to the values of INI file entries and HAL pins.

For example, if the INI file looks like so:

you may refer to the named parameters #<_ini[setup]xpos> and #<_ini[setup]ypos> within G-code.

EXISTS can be used to test for presence of a given INI file variable:

El valor se lee desde el archivo INI una vez y se almacena en caché del interprete. Estos parámetros son de solo lectura -asignar un valor causa un error de tiempo de ejecución. En código G los nombres no distinguen entre mayúsculas y minúsculas - son convertidos a mayúsculas antes de consultar el archivo INI. Por lo tanto, las entradas INI que contengan caracteres en minúsculas no son accesibles desde código G.

Example:

Access of HAL items is read-only. Currently, only all-lowercase HAL names can be accessed this way.

EXISTS can be used to test for the presence of a given HAL item:

Esta característica fue motivada por el deseo de una conexion más fuerte entre componentes de la interfaz de usuario como GladeVCP y` PyVCP` para actuar como fuente de parámetros para manejar el comportamiento del archivo NGC. La alternativa - pasar por los pines M6x y conectarlos - tiene un espacio de nombres limitado y no mnemotécnico y es innecesariamente engorroso como mecanismo de comunicación UI/Intérprete.

An expression is a set of characters starting with a left bracket [ and ending with a balancing right bracket ] . In between the brackets are numbers, parameter values, mathematical operations, and other expressions. An expression is evaluated to produce a number. The expressions on a line are evaluated when the line is read, before anything on the line is executed. An example of an expression is [1 + acos[0] - [#3 ** [4.0/2]]].

Los operadores binarios solo aparecen dentro de las expresiones. Hay cuatro operaciones matemáticas básicas: suma (+), resta (-), multiplicación (*) y división (/). Hay tres operaciones lógicas: o no exclusivo (OR), o exclusivo (XOR), y lógico AND). La octava operación es la operación de módulo (MOD). La novena operación es la operación potencia (**), elevar el número a la izquierda de la operación al exponente de la derecha. Los operadores relacionales son igualdad (EQ), desigualdad (NE), estrictamente mayor que (GT), mayor o igual que (GE), estrictamente menor que (LT), y menor o igual que (LE).

The binary operations are divided into several groups according to their precedence. If operations in different precedence groups are strung together (for example in the expression [2.0 / 3 * 1.5 - 5.5 / 11.0]), operations in a higher group are to be performed before operations in a lower group. If an expression contains more than one operation from the same group (such as the first / and * in the example), the operation on the left is performed first. Thus, the example is equivalent to: [ [ [2.0 / 3] * 1.5] - [5.5 / 11.0] ] , which is equivalent to to [1.0 - 0.5] , which is 0.5.

The logical operations and modulus are to be performed on any real numbers, not just on integers. The number zero is equivalent to logical false, and any non-zero number is equivalent to logical true.

Testing for equality or inequality of two double-precision floating-point values is inherently problematic. The interpreter solves this problem by considering values equal if their absolute difference is less than 1e-6 (this value is defined as TOLERANCE_EQUAL in src/emc/rs274ngc/interp_internal.hh).

The available functions are shown in following table. Arguments to unary operations which take angle measures (COS, SIN, and TAN ) are in degrees. Values returned by unary operations which return angle measures (ACOS, ASIN, and ATAN) are also in degrees.

The FIX function rounds towards the left (less positive or more negative) on a number line, so that FIX[2.8] =2 and FIX[-2.8] = -3.

The FUP operation rounds towards the right (more positive or less negative) on a number line; FUP[2.8] = 3 and FUP[-2.8] = -2.

The EXISTS function checks for the existence of a single named parameter. It takes only one named parameter and returns 1 if it exists and 0 if it does not exist. It is an error if you use a numbered parameter or an expression. Here is an example for the usage of the EXISTS function:

A line may have any number of G words, but two G words from the same modal group may not appear on the same line. See the Modal Groups section for more information.

A line may have zero to four M words. Two M words from the same modal group may not appear on the same line.

For all other legal letters, a line may have only one word beginning with that letter.

If a parameter setting of the same parameter is repeated on a line, #3=15 #3=6, for example, only the last setting will take effect. It is silly, but not illegal, to set the same parameter twice on the same line.

Si aparece más de un comentario en una línea, solo el último será usado; cada uno de los otros comentarios será leído y su formato será verificado, pero se ignorará a partir de entonces. Es de esperarse que poner mas de un comentario en una línea sea muy raro.

The three types of item whose order may vary on a line (as given at the beginning of this section) are word, parameter setting, and comment. Imagine that these three types of item are divided into three groups by type.

The first group (the words) may be reordered in any way without changing the meaning of the line.

If the second group (the parameter settings) is reordered, there will be no change in the meaning of the line unless the same parameter is set more than once. In this case, only the last setting of the parameter will take effect. For example, after the line #3=15 #3=6 has been interpreted, the value of parameter 3 will be 6. If the order is reversed to #3=6 #3=15 and the line is interpreted, the value of parameter 3 will be 15.

If the third group (the comments) contains more than one comment and is reordered, only the last comment will be used.

If each group is kept in order or reordered without changing the meaning of the line, then the three groups may be interleaved in any way without changing the meaning of the line. For example, the line g40 g1 #3=15 (foo) #4=-7.0 has five items and means exactly the same thing in any of the 120 possible orders (such as #4=-7.0 g1 #3=15 g40 (foo)) for the five items.

Muchos comandos hacen que el controlador cambia de un modo a otro, y el modo permanece activo hasta que algún otro comando lo cambie implícita o explícitamente. Tales comandos se denominan modales. Por ejemplo, si el refrigerante está encendido, permanece encendido hasta que sea explícitamente apagado. Los códigos G para movimiento también son modales. Si un comando G1 (movimiento recto) se da en una línea, se ejecutará nuevamente en la línea siguiente si hay una o más palabras de eje disponibles en esa línea, a menos que se dé un comando explícito usando las palabras de eje o cancelando el movimiento.

Non-modal codes have effect only on the lines on which they occur. For example, G4 (dwell) is non-modal.

Polar Coordinates can be used to specify the XY coordinate of a move. The @n is the distance and ^n is the angle. The advantage of this is for things like bolt hole circles which can be done very simply by moving to a point in the center of the circle, setting the offset and then moving out to the first hole then run the drill cycle. Polar Coordinates always are from the current XY zero position. To shift the Polar Coordinates from machine zero use an offset or select a coordinate system.

In Absolute Mode the distance and angle is from the XY zero position and the angle starts with 0 on the X Positive axis and increases in a CCW direction about the Z axis. The code G1 @1^90 is the same as G1 Y1.

In Relative Mode the distance and angle is also from the XY zero position but it is cumulative. This can be confusing at first how this works in incremental mode.

Por ejemplo, si tiene el siguiente programa, puede esperar que sea un patrón cuadrado:

You can see from the following figure that the output is not what you might expect. Because we added 0.5 to the distance each time the distance from the XY zero position increased with each line.

El siguiente código producirá nuestro patrón cuadrado:

As you can see by only adding to the angle by 90 degrees each time the end point distance is the same for each line.

It is an error if:

Commands are arranged in sets called modal groups, and only one member of a modal group may be in force at any given time. In general, a modal group contains commands for which it is logically impossible for two members to be in effect at the same time - like measure in inches versus measure in millimeters. A machining center may be in many modes at the same time, with one mode from each modal group being in effect. The modal groups are shown in the following Table.

For several modal groups, when a machining center is ready to accept commands, one member of the group must be in effect. There are default settings for these modal groups. When the machining center is turned on or otherwise re-initialized, the default values are automatically in effect.

El grupo 1, el primero en la tabla, es un grupo de códigos G para movimiento. Uno de ellos siempre está vigente. A ese se le llama modo de movimiento actual.

Es un error colocar un código G del grupo 1 y un código G del grupo 0 en la misma línea si ambos usan palabras de eje. Si un código G del grupo 1 que usa palabras de eje estaba implícitamente vigente en una línea (por haber sido activado en una línea anterior) y un código G del grupo 0 que usa las palabras de eje aparece en la línea, la actividad del código G del grupo 1 es suspendida para esa línea. Los códigos G del grupo 0 que usan palabras de eje son G10, G28, G30, G52 y G92.

It is an error to include any unrelated words on a line with O- flow control.

Los comentarios son meramente informativos y no influyen en el comportamiento de la máquina.

Se pueden agregar comentarios a las líneas de código G para ayudar a aclarar la intención del programador. Los comentarios se pueden incrustar en una línea usando paréntesis () o al final de una línea usando un punto y coma. El punto y coma no se trata como el comienzo de un comentario cuando está entre paréntesis.

Comments may appear between words, but not between words and their corresponding parameter. So, S100(set speed)F200(feed) is OK while S(speed)100F(feed) is not.

Here is an example of a commented program:

There are several active comments which look like comments but cause some action, like (debug,..) or (print,..). If there are several comments on a line, only the last comment will be interpreted according to these rules. Hence, a normal comment following an active comment will in effect disable the active comment. For example, (foo) (debug,#1) will print the value of parameter #1, however (debug,#1)(foo) will not.

A comment introduced by a semicolon is by definition the last comment on that line, and will always be interpreted for active comment syntax.

* (MSG,) - displays message if MSG appears after the left parenthesis and before any other printing characters. Variants of MSG which include white space and lower case characters are allowed. The rest of the characters before the right parenthesis are considered to be a message. Messages should be displayed on the message display device of the user interface if provided.

* (PROBEOPEN filename.txt) - will open filename.txt and store the 9-number coordinate consisting of XYZABCUVW of each successful straight probe in it. * (PROBECLOSE) - will close the open probelog file.

For more information on probing see the G38 section.

* (LOGOPEN,filename.txt) - opens the named log file. If the file already exists, it is truncated. * (LOGAPPEND,filename) - opens the named log file. If the file already exists, the data is appended. * (LOGCLOSE) - closes an open log file. * (LOG,) - everything past the , is written to the log file if it is open. Supports expansion of parameters as described below.

Examples of logging are in nc_files/examples/smartprobe.ngc and in nc_files/ngcgui_lib/rectange_probe.ngc sample G-code files.

* (ABORT,) - displays a message like (MSG,) with the addition of special handling for comment parameters as described below and of aborting the current running process.

* (DEBUG,) - displays a message like (MSG,) with the addition of special handling for comment parameters as described below.

* (PRINT,) - messages are output to stderr with special handling for comment parameters as described below.

In the DEBUG, PRINT and LOG comments, the values of parameters in the message are expanded.

For example: to print a named global variable to stderr (the default console window).

Inside the above types of comments, sequences like #123 are replaced by the value of the parameter 123. Sequences like #<named parameter> are replaced by the value of the named parameter. Named parameters will have white space removed from them. So, #<named parameter> will be converted to #<namedparameter>.

Parameter numbers can be formatted, e.g.:

will print the value rounded to an integer.

The formatting will be performed on all parameters in the same line unless changed, i.e., multiple formatting is allowed in one line.

The formatting string does not need to be right beside the parameter.

If the formatting string is created with the wrong pattern it will be printed as characters.

A G-code file must contain one or more lines of G-code and be terminated with a Program End. Any G-code past the program end is not evaluated.

If a program end code is not used a pair of percent signs % with the first percent sign on the first line of the file followed by one or more lines of G-code and a second percent sign. Any code past the second percent sign is not evaluated.

El intérprete y el planificador de tareas están cuidadosamente escritos para que el único límite en el tamaño del programa sea la capacidad del disco. Las interfaces TkLinuxCNC y Axis cargan el texto del programa para mostrarlo al usuario, y entonces la RAM se convierte en un factor limitante. En Axis, donde se dibuja la gráfica de vista previa por defecto, el tiempo de redibujo también se convierte en un límite práctico en el tamaño del programa. La vista previa se puede desactivar en Axis para acelerar la carga de grandes programas. En Axis, las secciones de la vista previa se pueden desactivar usando comentarios de control de vista previa.

The order of execution of items on a line is defined not by the position of each item on the line, but by the following list:

Use at least 3 digits after the decimal when milling in millimeters, and at least 4 digits after the decimal when milling in inches.

In particular, tolerance checks of arcs are done for .001 and .0001 according to the active units.

G-code is most legible when at least one space appears before words. While it is permitted to insert white space in the middle of numbers, there is no reason to do so.

Center-format arcs (which use I- J- K- instead of R- ) behave more consistently than R-format arcs, particularly for included angles near 180 or 360 degrees.

When correct execution of your program depends on modal settings, be sure to set them at the beginning of the part program. Modes can carry over from previous programs and from the MDI commands.

G17 use XY plane, G20 inch mode, G40 cancel diameter compensation, G49 cancel length offset, G54 use coordinate system 1, G80 cancel canned cycles, G90 absolute distance mode, G94 feed/minute mode.

Perhaps the most critical modal setting is the distance units—If you do not include G20 or G21, then different machines will mill the program at different scales. Other settings, such as the return mode in canned cycles may also be important.

Ignore everything in section Order of Execution, and instead write no line of code that is the slightest bit ambiguous.

Don’t use and set a parameter on the same line, even though the semantics are well defined. Updating a variable to a new value, such as #1=[#1+#2] is OK.

Line numbers offer no benefits. When line numbers are reported in error messages, the numbers refer to the line number in the file, not the N-word value.

Considere usar el modo de velocidad de tiempo invertido.

Because the meaning of an F word in meters per minute varies depending on the type of axis to be moved and because the amount of removed material does not depend only on the feed rate, it can be simpler to use G93, inverse speed of time, to achieve the removal of desired material.

Because the meaning of an F-word in feed-per-minute mode varies depending on which axes are commanded to move, and because the amount of material removed does not depend only on the feed rate, it may be easier to use G93 inverse time feed mode to achieve the desired material removal rate.