In a method of controlling operation of a processing system, a host computer, a process tool and a component of an evacuation system, for example an abatement tool, are connected to a system bus. The abatement tool monitors signals transmitted on the system bus between the host computer and the process tool, and signals received directly from the process tool. The abatement tool uses information contained within the monitored signals to generate a signal for the process tool regarding an operating characteristic of the abatement tool. This signal is transmitted either directly or over the system bus to the process tool, which uses the generated signal to control an operating state of the process tool.