if/while ?

All the "while" knows is to execute what ever code you have between the while/endwhile or to skip the code between the while/endwhile.

John

piasdom wrote:

thanks andypugh, but i can't figure out what goes in the [ ].
i understand #2 = [#2 - #3] equaling -.01, so it would move down .01 each pass(or run of code)?

Exactly.

but no idea what [#2 GT #1]
i'm guessing GT is GoTo. what does the While ? xy or z?

No, GT means "Is Greater Than"
So, that loop which I wrote out carries on looping between the DO and the WHILE as long as #3 (a variable) hasn't hit the limit depth stored in #1

The two O100 codes indicate that the DO and the WHILE are a pair. They could be any number, but it seems traditional to use O100, O101 and so on.
DO / WHILE always runs once, and then runs again if the conditional statement in the brackets after the WHILE is true. There is an alternative form, WHILE / ENDWHILE which checks first, and can run zero times.

Other bits of G-code between the DO and WHILE or the WHILE and ENDWHILE alter the variables and use them to set the Z depth, or anything else. All the loop does is repeat a block of code "while" a condition is true.

piasdom wrote:

well, i ran this. had to change <> to () at end to be able to run.

Ah, well, you see, the stuff I put in <> characters was meant to indicate where the actual G-code to do the machining was meant to go, I rather assumed you already had that written.

it ran but only once at z-.1, which is right.
but shouldn't it have ran till Z got to -.4
cutting the square at each level of .1 ,.2, .3 and .4 ?

Not the way it is written. I think that is my mistake, you need #1 = -0.4

A DO-WHILE loop does the code then checks the while condition. A WHILE-ENDWHILE loop checks the while condition and if true does the code.

So a DO WHILE loop in sudocode

Do

Stuff
...

Check While condition if true return to top and run again



A WHILE ENDWHILE loop in sudocode

Check While condition if it is True run code if False skip code

Stuff
...

Endwhile

So your do while loop will always execute at least once. Your test condition is while #2 is greater than #1 so it has to be larger before the loop stops. In other words you must pass up your desired target before the loop exits.

You either have to change your relational operator to one that gives you the correct outcome or the loop.

Hidden in the Binary Operators are the Relational Operators.

www.linuxcnc.org/docview/html/gcode_over...sub:Binary-Operators

John