If you're in the Bay Area, my work has a lab of fairly expensive
scopes and digital signal analyzers. Though it probably
is some very simple rs-232 like protocol with that DC offset.
I'm using mine for radiant hydronic, so getting data on usage
and cycles would be nice, though it might be easier to
use a fancier thermostat (thermostat turns on 2 pumps
which triggers the Takagi)