Periodic event-triggered control (PETC) [13] is a version of event-triggered control that only requires the measurement of the plant output periodically instead of continuously. In this note, we present a construction of timing models for these PETC implementations to capture the dynamics of the traffic they generate. In the construction, we employ a two-step approach. We first partition the state space into a finite number of regions. Then, in each region, the event-triggering behavior is analyzed with the help of linear matrix inequalities. The state transitions among different regions result from computing the reachable state set starting from each region within the computed event time intervals.