A plurality of serially addressable devices connected to transmit data to or from a central controller via a two-wire polling loop has a global poll capability. The transmissions of data are via a tri-level line signal to provide both power and data transmission on a two-wire line. Global polling is...http://www.google.ca/patents/US5347515?utm_source=gb-gplus-sharePatent US5347515 - Method and apparatus for global polling having contention-based address identification
