  Reversible Probabilistic Cellular Automata are a special class of automata
whose stationary behavior is described by Gibbs-like measures. For those models
the dynamics can be trapped for a very long time in states which are very
different from the ones typical of stationarity. This phenomenon can be
recasted in the framework of metastability theory which is typical of
Statistical Mechanics.
  In this paper we consider a model presenting two not degenerate in energy
metastable states which form a series, in the sense that, when the dynamics is
started at one of them, before reaching stationarity, the system must
necessarily visit the second one. We discuss a rule for combining the exit
times from each of the metastable states.
