RE: Why can't I re-run this program?

From: Alan Marconett KM6VV <KM6VV@...>

>Hi Ray,
>
>Thanks for the comments. <s> I guess the "programmer" in
>me wants to think about reusable code, modularity, ease of
>understanding, etc.

Don't we all! If you chase down the roots of G-code variation in
commercial machines it comes down to sales posturing. "With the
competition's machine you will have to write 20 blocks of code. With ours
you can do it in one!" <g> There have been positive results to the
language from some of this but it does tend toward confusion.

If you chase down the roots of the "hobby" grade controllers, most started
with bright folk who had a dream and wrote some code. Most of these were
less interested in rigorous interpretations of RS-274 motion control
language than they were in making their software and hardware work. The
result is everything from HPGL -> dxf -> a g-code flavor -> conversational.

>I was also wondering about conditional statements; if we have labels for
>subroutines, do we have something in NGC or another "flavor" Gcode? We
>could use labels for "jumps", i.e., "#IF V200 = 0 GOTO P20", Ok, the
>syntax is not there yet (make it look a little like basic?). The V200
>would be the variable, and P20 would signify the point in the program
>that is labeled $20. Possibly "G23 #200 = 1.200 P20"?

There are conditional (boolian) statements available in the NGC interpreter
but they aren't be used for jumps or loops. The line numbers are not used
for anything except reference to humans. Variables are subject to math
and can be applied to distances and codes but again there is no good way
within the interpreter itself to use them for jumps.

IMHO - NIST has taken g-code interpretation about as far as it wants and
needs with the current six axis system. For the future they seem to be
looking to other approaches to translate geometry or real or drawn objects
into machine motion. (There are a bunch of interesting papers on their
site)

HTH

Ray