1. A diagnostic system for use in a process plant having a process control system that performs manufacturing related control functions with respect to the process plant and a safety system that performs safety related control functions with respect to the process plant, comprising: a computer having a processor and a memory; a process control system controller communicatively coupled to the computer and adapted to perform process control functionality using one or more process control field devices; a safety system controller communicatively coupled to the computer and adapted to perform safety system functionality using one or more safety system field devices; and a diagnostic application stored on the memory of the computer and adapted to be executed on the processor to enable one or more users to perform a diagnostic activity with respect both the process control system and the safety system, the diagnostic application including a communication routine adapted to communicate process control system messages to or from the process control system controller and to communicate safety system messages to or from the safety controller, wherein the process control system messages and the safety system messages use a common communication format including a field that distinguishes the process control system messages from the safety system messages.