OK. There are 3 different versions of Nano:
Nanosynth
http://gbdev.gg8.se/files/musictools/Ol
Nanosynth/
Nanovoice
http://gbdev.gg8.se/files/musictools/Ol
Nanovoice/
and Older? First? version of Nanosynth (called Nanovoice) (with source code in C)
http://swiki.hfbk-hamburg.de/MusicTechnology/132
Nanosynth can't be synced via some clock (serial port of Gameboy) ...
Nanovoice can be synced in the same way as Old Nanoloop, as E.S.C. mentioned...
About First version of Nanosynth/Nanovoice (from one of my old posts):
The only difference against the other Nanosynth rom is, that when you hit Start, it doesn't switch between mono / stereo delay mod, but it switches between normal / sync mod
in Sync mod it waits for triggering:
I remember that connecting 2 of GB serial's pins triggers a note, disconnecting these pins triggers another note etc...
You can try it alone, or I can try it same as you from a scratch
There was (maybee!) some other thing to do, connect one of another pins to ground. I actually don't remember that. It's more than year I tried to work with this rom.
...