  In this paper we study an one-dimensional two-species exclusion model with
open boundaries. The model consists of two types of particles moving in
opposite directions on an open lattice. Two adjacent particles swap their
positions with rate p and at the same time they can return to their initial
positions with rate q if they belong to the different types. Using the Matrix
Product Ansatz (MPA) formalism, we obtain the exact phase diagram of this model
in restricted regions of its parameter space. It turns out that the model has
two distinct phases in each region. We also obtain the exact expressions for
the current of particles in each phase.
