I've been messing around with trying to get multiple files to work together in Sourcecode 3 with z80 Assembly, but I would like to know the "Proper" way of doing things, because I keep getting error messages and stuff not working.
What I want to do:
Have 3+ files: One for 'main' (runner program)
One for 'data' (labels and such)
One or more for 'routines' (the main actions the program will take)
I want to be able to include "ti83plus.inc" just once and then have all the routine files be able to 'see' it so that I may use bcalls and such in my routines. I've found a couple online resources for linking files like this, but none gave ALL of the nessecary code, so that's why I'm asking for the "Proper" way to do it.
I would like to know exactly what to put in each file, and an explanation of WHY everything needs to be that way. Thank you for all your time and patience. My end goal is to make a knock-off of Call of duty zombies once I get good enough at assembly, but I just started learning this week, so that's probably a long ways away.

Code:

What should I put at the top of my routines and data? or should I just write the labels straight away?

You don't *need* labels at the top of the other files. It just adds the code to the main program where you include it. However, if you include it at the bottom (recommended), you need labels to call the routines or to use the data.

Ah okay so If I included my routines file at the top of my main file it would just start executing the code there before the code in my main file?

Exactly! And if you put data at the top of the main file, it executes data. Funny, isn't it?

When I put my include statements at the bottom of my main file, It can't find the labels in my routines file??? I don't understand why It does that.

How do you include it? If the name of your secondary program is "DATA", use #include "DATA.asm".

I wrote
In main:
...
call testPrint
...
#include “routines.asm”

In routines

testPrint:
*code to print a char that I have confirmed works*