  In this paper we analyse the non-wandering set of 1D-Greenberg-Hastings
cellular automata models for excitable media with $e\geqslant 1$ excited and
$r\geqslant 1$ refractory states and determine its (strictly positive)
topological entropy. We show that it results from a Devaney-chaotic closed
invariant subset of the non-wandering set that consists of colliding and
annihilating travelling waves, which is conjugate to a skew-product dynamical
system of coupled shift-dynamics. Moreover, we determine the remaining part of
the non-wandering set explicitly as a Markov system with strictly less
topological entropy that also scales differently for large $e,r$.
