The adsorption of binary mixtures on solid heterogeneous substrates is studied by Monte Carlo simulation in the framework of the lattice gas model. The energy of the surface has been modeled by considering two kind of adsorption sites, deep and shallow traps, forming square homogeneous patches of different sizes; these adsorption domains have been distributed either at random or in chessboard-like lattice to obtain simple heterogeneous topographies. The adsorption process has been monitored through total and partial isotherms and differential heats of adsorption corresponding to both species of the mixture, for different values of the parameters involved in the model (lateral interactions, energy gap between deep and shallow patches) and different topographies. A rich variety of behaviors is found and analyzed in the context of the lattice gas theory.