That address is typically an “O” word, but many controllers have the option of looking for an “N” word if the O# is not found. – Where do I find the subprogram? There is a word (most often the “P” word) that provides the address. While there are a lot of different styles, they’re mostly just slightly different ways of saying the same things: Here is G-Wizard CNC Simulator and Editor’s screen for setting up your controller’s syntax: Subprogram Call Syntaxĭepending on your controller, there are a number of different syntaxes available for Subprogram calls. When it hits an “M99” in the subprogram, that causes it to return to the main program right where it left off and keep going. When it hits M98, execution jumps over to the subprogram. The call to the subprogram is “M98”, which takes a parameter telling it the “O” number where it can find the subprogram. Your program might look like this:Īs you can see, the main program and the subprogram each have their own “O” number. First, stick the g-code for the subprogram under its own subprogram number–its own “O” number. A subprogram call is pretty straightforward. Let’s start out with Subprogram Calls, because they’re a little simpler to understand than Macro Calls, albeit less powerful. Pretty cool trick! M98 and M99 G-Codes: Subprogram Calls Why repeat the same path for each level? GibbsCAM generates g-code that generates the path for a level once as a subprogram and then calls it multiple times after setting the z-level deeper each time. Consider the process of milling a pocket by stepping down several levels and cutting the same toolpath. Even if you’re not trying to reuse code, using calls can make your existing code much smaller and easier to understand. If you have a big library of powerful snippets, you’ve got the potential for some real productivity enhancement. It’s kind of like delegating responsibility to that code snippet. You “call” that code, it does its thing, and then it “returns” to your main program to continue executing right after the call. Think of each as a way to access code sequestered in its own little mini-program. The G-Code language provides two different methods for doing this: subprogram calls and macro calls. To make g-code convenient for re-use, we need some way of centralizing it and then accessing it from the part program. First thing that happens is you need to change the code, perhaps to fix a bug, but you have copies of it scattered everywhere.
You could try copying and pasting your code everywhere to reuse it, but that’s a mess. In the article on Parameterized Programming, we learned how to modify g-code so it can be used in many different situations through the use of variables.
M98 & M99 G-Code: CNC Subprograms & Macro Calls CNCCookbook’s G-Code Tutorial Subprograms and Macro Calls for Code Building Blocks
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