Chiptunes are partly defined by lack of polyphony as far as composition goes, for instance the NES or gameboy had 5 monophonic channels. A triangle wave generator, two variable width pulse generators, noise, and a really lofi sample channel that was usually used for percussion. The lack of polyphony means no sustained chords(well you could play one triad at a time but nothing else with it), so lots of arpeggiation, counterpoint, and riffs and a lot of the music was characteristically melodic where a lot of game soundtracks these days go out of their way to not be melodicā¦modulation effects are also very important when you have just a few simple sounds, really utilize vibrato and tremelo. Pokemon RedBlueYellow is one of my favorite gameboy examples, lots of good use of vibrato in that soundtrack especially
Radian: I didnt try it yet. I will look at the manual, thank you.
Shadowpsyc: Thank you! Great starting point. So chords are not needed to create great music :-).
- So you are saying that chiptunes are based mainly about used sounds, not about composition.
Indeed. Regarding sounds and pitfalls, I think the fastest way of making chiptune sound non-chiptune is to use normal pads instead of arps or very simple pads. Too modern drum samples is also a give-away (unless lofi filtering). At least it doesnāt provide the style I associate with āchiptuneā.
- Why Milky Tracker and not Renoise?
I know both and i know that Milky Tracker is more used for chiptunes (or famitracker) but i dunno why.
The simple answer is that Iām used to Milkytracker. Doing the same in Renoise as I do in Milkytracker would take too much time due to bad workflow. Setting up vibsweep and detune delays is too much of a hassle, for instance. Also, the restrictions in Milkytracker are good and the possibilities of Renoise can easily tempt me to divert from the chiptune sound. Be careful of dsp effects - the general rule would probably be that more dsp effects can be used the more simple the arrangement is.
ā¦Setting up vibsweep and detune delays is too much of a hassle, for instanceā¦
What is vibsweep and what do you mean with detuned delays? Sorry for the noobish questions 
The lack of polyphony means no sustained chords(well you could play one triad at a time but nothing else with it), so lots of arpeggiation
Aaaand, in true chip fashion that would be achieved with the arpeggio command 
A37 (Minor))
A47 (Major
etc.
The arpeggio works in tick rate - usually, 12 times per line.
^And you can now make super-arpeggios with phrases.
What is vibsweep and what do you mean with detuned delays? Sorry for the noobish questions
Vibsweep means the vibrato depth is increasing after time. XM has it as an instrument setting, and itās possible to make in Renoise since V3 by using the pitch envelope.
Detuned delays means the āechoesā are slightly detuned (like Ā±8 cents). It will make them sound more spatious, especially when panned left and right.
38911 Bytes is a great little C64 chip VSTi for free:
http://theodosynthsarchive.wordpress.com/category/38911bytes/
I made the little tune below in a spare 20 minutes restricting myself to just 3 tracks with no effects to make it C64 authenticā¦
Yes. Chiptune music rules!
(also - donāt forget to turn off interpolation when working with lofi samples)
Also donāt forget a lot of real chiptunes used actual synthesizers. There might well be some lo-fi going down due toā¦ whateverā¦ but maybe not re-pitched sample grunge/aliasing. The chip referred to is a synthesizer on a chip.
Vibsweep means the vibrato depth is increasing after time. XM has it as an instrument setting, and itās possible to make in Renoise since V3 by using the pitch envelope.
Detuned delays means the āechoesā are slightly detuned (like Ā±8 cents). It will make them sound more spatious, especially when panned left and right.
Thank you
Also you can change the song playback choosing SONG playback & compatibility option from Renoise to Amiga/FT2.
38911 Bytes is a great little C64 chip VSTi for free:
http://theodosynthsarchive.wordpress.com/category/38911bytes/
I made the little tune below in a spare 20 minutes restricting myself to just 3 tracks with no effects to make it C64 authenticā¦
Did you know that Odo, creator of this synth, uses Renoise?
I had wet dream onceā¦ Odo created native synth for it 
if you compose a song in goattracker, then you have made a chiptune, mostly
Love the digidrums on that goattracker tune!
Some Atari ST demos used this before soundtrack was portedā¦
I mean Soundtrackerā¦ No edit button?
Wonāt be able to sleep knowing that typo is thereā¦
lolz, had to check if goat tracker was ported to android and found this:
Goat Tracker https://play.google.com/store/apps/details?id=com.sbumpkin.goat
Description
Goat tracker is an application to help a farmer track when a goat should come into heat based on the last heat date.
If the farmer has bred the goat then it will calculate the earliest date to draw blood to check for pregnancy.
If the goat is pregnant it will calculate the approximate due date.
This is bound to be a long rant from me. Sorry about that 
The short version:
Regarding rules/restrictions for chipmusic. I feel that is something that is constantly evolving so in the end the most important thing is that the music feels right. Keep it simple. Arpeggios are you friend
The long version:
The thing is, chipmuisc is not ONE specific soundā¦
When I started making chip music on the Amiga back in the day the guidelines I went by were pretty much given: .mod-fileformat and 4 channels were the general hardware and software restrictions of the time. On top of that you should try to keep the final file size south of 20kb.
The file size restriction pretty much eliminated decently sampled instruments so instead youād draw your own little waveforms by hand since the software did not generate stuff like that for you.
The channel restriction pretty much forced you to use arpeggio-chords since each note took up one channel, and you only had four to work with.
So those were the first restrictions I worked with.
Here you have some good examples of the Amiga 4chn mod-chip sound:
Radix āPaul the penguinā: https://www.youtube.com/watch?v=CsAPmo-fkqE
4-Mat āLFFā: https://www.youtube.com/watch?v=zlUFYMRNkPw
Emax āDigital bass-lineā: https://www.youtube.com/watch?v=m1-fVb9vZDE
Later I moved from Amiga to PC. To begin with I continued working with my old restrictions but after meeting a fellow PC chip composer at a demoparty I got encouraged by his multichannel .xm-tunes to evolve.
On the PC you could use up to 32 channels. And on top of that the .xm-format gave you more effect columns and volume/pan envelopes which made it easier to tweak the sounds.
The file size got a bit bigger with the additional channels but nothing crazy. I seem to recall thinking one of my tunes that ended up about 100kb was humongous
I continued working with about the same sorts of tiny hand drawn waveforms so that part of the sound was pretty much intact. I fondly remember when I used a sampled cymbal in one song and my fellow chip musicians of the time were not too keen on that addition to the sound. ā¦so that experiment went out the window pretty fastā¦ 
With the 4 channel restriction lifted I often used ārealā chords in combination with the arpeggios. That together with enough channels to make echoes as well as phaser/flanger like detune tricks made the .xm-tunes sound more refined and bigger than the Amiga tunes.
Here are a few good examples of the PC multichannel xm-sound:
Radix āThe Missionā: https://www.youtube.com/watch?v=QQxo9WG7Ktk&list=UUYZIBGsbFxj9EDsaU67oJ-g
Loonie āContemplatedā: https://www.youtube.com/watch?v=IXzAjQeLD08
Zabutom āFinal Blastā: https://soundcloud.com/zabutom/final-blast
I had along brake from chip music between 2000-2010. When I finally came around and felt like doing some stuff again I took a look around to see what had happened the last decadeā¦ And things had changed a lot Softsynths, tweaked gameboys, post processing and stuff like that.
Now a days I donāt care much about file restrictions. I often use fitting samples regardless of size, but I mix and match with old style hand drawn waveforms.
Lately I have started doing some post simple processing and mixing outside the tracker to give the tunes a bit more clarity and punch. Thats something I never did back in the day but since mixing in the tracker can be cumbersome I finally ended up going the āeasy routeā
Since I tend to enjoy working with layers I mostly use lots of channels but now and again I want to challenge my selfe and then I go back to the 4 channel restriction.
ā¦but the thing isā¦ I entered a old school music comp last year and thought it would be fun to use the 4 channel less than 20kb restriction so I went for it. Managed to do a song like that and entered the comp. ā¦and at the party I was talking to a c64 guy about my tune and me working with restrictions. He just smiled at me because on the c64 you only have 3 channels and less memoryā¦
Soooā¦ Chipmusic and the chip sound is not just ONE thing. Not just one set of restrictions. Just try to keep it simple and have fun.
If you are interested here are some chiptunes I have made:
4 channels .xm: https://soundcloud.com/gusse_dsx/cracked-nostalgia
4 channels .xm: https://soundcloud.com/gusse_dsx/dandelion-shuffle
4 channels .xm: https://soundcloud.com/gusse_dsx/minor-problem
12 channels .xm: https://soundcloud.com/gusse_dsx/digital-vacation
24 channels .xm: https://soundcloud.com/gusse_dsx/legacy-system-anthem
24 channels .xm: https://soundcloud.com/gusse_dsx/intergalactikus
32 channels .xm: https://soundcloud.com/gusse_dsx/rusty-robot