FSM-based Digital Design using Verilog HDL

10

Introduction to Petri Nets

10.1 INTRODUCTION TO SIMPLE PETRI NETS

The Petri net is a state diagram that can be used to describe the behaviour of both sequential and parallel systems. It was initially conceived by Karl Petri in the 1960s and has had a good following of academics ever since. There is a website devoted to all things Petri at http://www.informatik.unihamburg.de/TGI/PetriNets/.

Petri nets are often used as a tool to study the behaviour of parallel and concurrent systems (not necessarily electrical). They have also been used to study parallel and concurrent programming methods. In recent years, researchers have shown [1] how the Petri net can be used to develop and synthesize electronic FSM systems, in a similar way to how synchronous and asynchronous systems can be developed and synthesized. The main reason for employing Petri nets is the ability to create parallel systems. The following method makes use of material with permission from [1].

Figure 10.1 illustrates a two-state diagram and its Petri net equivalent. In a Petri net, the ‘state’ is represented by a ‘placeholder’ and the ‘transitional lines’ between states are represented by ‘arcs’ that connect the placeholder (P1 and P2) to transition points (T1 and T2). The inputs along the transitional lines of a state diagram are placed against the transition points along the connecting arcs that link one placeholder to another in a Petri net.

The Petri net uses a memory element to represent each placeholder (rather ...