This is maybe not the best place to post this, but hopefully someone like nitro, oliver or johan (or some other gameboy wizard) sees this..

So according to gbatek and the official Nintendo GBA programmers manual, it isn't possible to sync a DMG/CGB with a GBA running a GBA program, because the GB's serial port operates and 5v and while running a GBA cart, the GBA's is at 3.3V. (Although if a GB cart is inserted in a GBA, the  serial port runs at 5v, so you can for example sync 2x lsdj's if one is on a GBA.)

I'm writing a GBA program that I want to be able to sync to LSDJ running on a DMG/CGB/GBA/whatever, so I was thinking the only way to sync it properly would be using a 5v->3.3v converter ic, which isn't really a big deal. The alternative being it just wouldn't work right, or potentially frying the GBA i/o with an unexpected 5V...

However, I've heard that it is actually possible to sync nanoloop2.x, (which is a GBA cart) running on a GBA, to LSDJ running on a classic GB.. So the question is; does nanoloop use some magic undocumented register in order to trick the GBA into the 5v mode? Or does the 5v signal just somehow work even though it should be 3.3v, and even though nintendo explicitly warns against doing this..? Does anyone have any experience trying this, did the GBA act weird in any way?

Yeah it's a complicated question! I don't really have the right hardware right now to test this, and just thought I'd ask before trying.


I don't have a whole lot of insight on this... but I have attempted the nl 2.x + LSDJ on DMG sync. It does work, but one of the game boys ends up emitting an awful (and quite loud) hum. I've always assumed this was due to the voltage difference, but I'm not entirely sure.

I also have heard of people performing the sync without this issue, though. perhaps it depends on the nanoloop 2 version. maybe some versions of nl 2 have a fix for the voltage difference?

edit: this was nanoloop 2.7 on a normal GBA, for clarification

Last edited by Kedromelon (Mar 10, 2015 9:57 pm)


Yeah I was kinda hoping there was some magic fix in the nl2 carts, but sometimes it works and sometimes it doesn't which makes me think there isn't. It would be nice to get a definitive answer about that though!

Oh, only just noticed this old thread … 26-w-lsdj/

It seems like people have less problems using a color game boy as the host, which doesn't really make any sense as CGB/DMG should both be the same voltage!


I had no problem syncing :
- LSDJ on DMG and nanoloop 2.3/2.5 on gba sp
- nanoloop 1.6 on DMG and nanoloop 2.3/2.5 on gba sp
- nanoloop 1.6 on gba sp and nanoloop 2.3/2.5

Or maybe I have missed one thing, but I don't think.


I think its the way nanoloop syncs are just high/low pulses, and not actual data. Closer to dinsync than a serial connection like midi clock. So it doesnt matter the voltage you are just counting on off states.

Unsubscribe … ca-how-to/