In this paper we investigate Timed Petri nets (TPN) with fixed, possibly zero, durations and maximal step semantics. We define a new state representation where a state is a pair of a marking for the places and a marking for the transitions (a matrix of clocks). For this representation of states we provide an algebraic state equation. Such a state equation lets us prove a sufficient condition for the non-reachability of a state in a TPN. This application of the state equation is subsequently illustrated by an example.