A communications control method whereby a "master" station asks many devices attached to a common transmission medium whether they have information to send. Polling provides a very simple method to retrieve data from various control and monitoring systems. The Master or Host explicitly makes a request for data, and the Slave system replies. The process repeats for each data request. Data that changes between polling requests is lost. The alternative to polling is a report by exception mechanism whereby information is sent as soon as a change is detected.