In the present paper, the problem of additive cellular automata is pos
ed as a second-order linear difference equation in two indices-time st
ep t and position i subject to a periodicity condition for all t and a
n initial condition for t = 0. An explicit solution of this mathematic
al problem is obtained by using the method of generating function. Thi
s explicit formula enables us to compute the configuration at any time
without any explicit simulation. The explicit formula has been derive
d for all important additive rules; with the help of these, many salie
nt characteristics of the transition may be obtained with surprising e
ase. The explicit formula method appears to be very efficient and has
possibilities to be applied to diverse situations in cellular automata
theory.