  A driven diffusive model of three types of particles that exhibits phase
separation on a ring is introduced. The dynamics is local and comprises nearest
neighbor exchanges that conserve each of the three species. For the case in
which the three densities are equal, it is shown that the model obeys detailed
balance. The Hamiltonian governing the steady state distribution in this case
is given and is found to have long range asymmetric interactions. The partition
sum and bounds on some correlation functions are calculated analytically
demonstrating phase separation.
