  Configuration space of abelian gauge theory on a periodic lattice becomes
topologically disconnected by excising exceptional gauge field configurations.
It is possible to define a U(1) bundle from the nonexceptional link variables
by a smooth interpolation of the transition functions. The lattice analogue of
Chern character obtained by a cohomological technique based on the
noncommutative differential calculus is shown to give a topological charge
related to the topological winding number of the U(1) bundle.
