Apprentice Siemens user questions!

Hi guys! I am an aspiring CNC technician (apprentice). I am currently doing training in the aerospace sector and the machines we are using run Siemens 840d. I am starting to understand the various commands that the machine we are using executes and what they mean. I am definitely a novice so enjoy my entry level questions!

I am wondering?:

1. Are G codes a standard (are they the same across all machines) ?

2. Are M codes a standard (are they the same across all machines) ?

3. If they are machine specific where would I go to find these listed with meanings? For example we have a siemens 840d operating manual, would I be able to find these common conventions listed in there? Where do you veteran machinists go to understand code you haven't come across before?

There are G/M code standards for most of the codes. The basic codes are pretty much standard across all manufactures, but each manufacturer has their own codes for some special functions.

Here is a good place to start for a general understanding https://en.wikipedia.org/wiki/G-code

G-codes are not specific for certain machines.
G-codes are (nearly) the same for all controls. But be aware that only the basic G-codes (e.g. G0, G1, G2, G3, G4 etc.) are the same for controls of different manufactures.
Siemens has a lot of G-codes which don't look so at a first glance.
For example in the G-code group defining the type of a curve you will find the traditional G-codes for defining straight lines and circles (G0, G1, G2, G3) but also G-codes named ASPLINE, BSPLINE, and CSPLINE for defining different spline types. It would have been possible to name these G-Codes in the traditional way with the letter G and a number, for example G170, G171, G172, but Siemens preferred to use more speaking names.

The situation with M-codes is different.
Only a few M-codes are standard for most controls (M0 - M6, M17, M19, M30).
All other M-codes are machine specific. A M-code is basically a switch which you can set. The NC-control will set an output (to be read by PLC) but it doesn't know its function.
So you can look at M80 as a command which sets output number 80 and what ever is connected to this reacts correspondingly e.g. a pump is started or a door is opened or closed.
Which function of an M-code is defined in the PLC programme.

A List of G-Codes you will find in the Siemens manuals (see below).
M-Codes should be listed in the manuals provided by the manufacturer of your machine.

From Siemens there is quite a number of manuals available online. Try the following link as a starting point:
https://support.industry.siemens.com...anual&lc=en-WW

Thank you very much guys, I shall look into this more!