This paper concerns the asymmetric transport associated with a low-energy interface
Dirac model of graphene-type materials subject to external magnetic and electric
fields. We show that the relevant physical observable, an interface conductivity, is
quantized and robust to a large class of perturbations. These include defects that
decay along or away from the interface, and sufficiently small or localized changes in
the external fields. An explicit formula for the interface conductivity is given by a
spectral flow.