I have finally gotten an assembler working on my laptop so i have decided to venture out into the world of asm again. And I was going to go ahead and try to create sample programs from what i learn in 28 days, and also post some of the code used in that tutorial with comments on how i think it works. Then someone could possibly explain if i am on the right track or something similar.

Edit:Thanks to bfr and b-flat, my previous question has been solved so i will just go ahead and post how i think the code is working.

The Code:

Code:


Edit 2: Here is my attempt at 2d arrays. For some reason though it returns 9 instead of 10 like i thought it should.


Code:

0+(18/2) = 9. What's puzzling about that?

Where did you get the 0 and the 2, and i guess the 18 comes from what is loaded into de?

You're starting at index zero. Because you wrote .dw, not .db, each of the numbers in your table takes two bytes. Therefore, if 0 is at byte 0, 1 is at byte 2, 2 is at byte 4..., and 9 is at byte 18 (and 19, of course). Got it?

Makes sense, and if my next question sounds really stupid sorry. If i used db instead of dw would the result be 10?

No, the result would be 18. .dw means every number takes 2 bytes, so if .db means every number is one byte, byte 0 contains 0, 1 contains 1, blah blah blah 18 contains 18.

Alright it makes a little more sense. Let me go mess around with the code a bit more and see what kind of values i can get to help me out.

Edit: It seems as though the tutorial in 28 days doesn't even follow its own formula(at least to me) so i am going to attempt to code it myself and see if that may help a little.

Edit 2: Here is my attempt at finding the address of an element in a 2d array. For some reason though it appears to be returning an address and not the number. Also sorry in advanced if i am being frustrating.


Code:


Edit 3: Well i just decided to load 10 into e and that gave me 5 like it should, now i just have to figure out how to get 10 out of (2,2).

Edit 4: Yes another edit I have found out i cant do what i wanted to do in edit 3 until i learn how to do loops so for now i have to do the math manually.

For some reason asm is starting to make a lot more sense to me than it did now. Finding numbers in an array is even really easy and makes tons of sense. Back in the day(two years ago) i couldn't even make heads or tails out of anything. Don't know why, but just to show how much of a noob i was here is a post where i even managed to make the most of the time calm Kerm frustrated http://www.cemetech.net/forum/viewtopic.php?t=1230&postdays=0&postorder=asc&start=0

Wow, no offense, but you were such a n00b back then. Your spelling and grammar has improved significantly, as has your tact in asking questions. I still repeat my suggestion from back then to really understand z80 before diving too far in. I also unlocked the thread you linked to; dunno why it was locked.

I don't know why it was locked either, but it seems almost all of the threads are. Also thanks for the compliment, and i am following your suggestion this time.; just take a look at my first post . Plus this time around i am going in without the thought of making a super great game.

Sorry about double posting but i have gotten to the write back tutorial and i wanted to make sure i absolutely understood what was going on before i continued any further. Here is the code with my comments, someone please correct me if i am wrong.


Code:

yeah, it looks right, but that could be because its a copy/paste of learn z80 in 28 days

I know the code is right and it works i was wondering if my explanation of why it worked by commenting was correct.

Looks right to me. Now, by looking at all the little instructions, can you figure out what the whole program will do when you run it? (That is, if 28 days didn't already tell you.) The crux of assembly is that individual instructions can do almost nothing on their own, but you need to see how they come together to do big things.

Indeed, answer magicdanw. for example, what's with the datastart-$9d95+4 line?

Although this may have nothing to do with the whole purpose of the program, but about this section of code:

Code:

Couldn't it be changed to this instead to save space and/or speed?

Code:

Since you will be swapping hl with de, and then overwriting hl with DataStart, couldn't you add to hl to de instead of the other way around (since addition is commutative, the end product will stay the same)? Or am I missing something since I haven't even gotten past Day 7 of the tutorial?

hl is the two-bit accumulator of sorts, meaning it is the only one that you can add to.

There's no such command as add de,hl. You always have to be adding a=a+* (8-bit) or hl=hl+* (16-bit).

Oops, I meant to say two-byte, or sixteen-bit. Thanks for covering, Kerm

A few notes about comments (some have already been pointed out):

Try to find generalizations of a section of code instead of single instructions.

(my preference, but you don't have to do it) make comments as small (few words) as necessary.

try to find things not obvious and comment on those.

don't be afraid to use blank spaces in the source to seperate blocks of code. it will make it easier to read, and doesn't affect the final negatively at all (in fact, it should allow you to right better code).

Put comments on labels (especially for data/defines) so you and others know what they are used for.

ex: (from your code)

Code: