Patent ID: 6373376
Filing Date: 2002-04-16
Classification: G05B,H04B,H04J,H04L

Abstract:
In a system of the type having a plurality of nodes for communicating with each other through messages carried by a data signal comprising a series of data bits sent and received on a data line respectively to and from a data terminal of each node connected to the data line, said data bits encoded in dominant and recessive signal levels of the data signal corresponding to binary values and by which each said node resolves collisions of messages sent by more than one node, each said node for receiving an AC waveform at an AC power terminal from an AC power line, wherein each said node includes:a) a power supply for providing DC power at first and second DC power terminals for operating the node and for communicating through the data line with the other nodes, said second DC power terminal voltage level corresponding to the dominant signal level; b) an interface circuit comprising i) a pull-up impedance connected between the first DC power terminal and the node's output data terminal, and ii) a variable impedance connected between the node's output data terminal and the second DC power terminal and having a control terminal, said variable impedance providing a first impedance value substantially smaller than the pull-up impedance value responsive to an output data signal at the control terminal having a first level, and an impedance substantially larger than the pull-up impedance value responsive to a second level of the output data signal at the control terminal, wherein said variable impedance's first impedance value holds the data line voltage level substantially at the dominant signal level irrespective of the impedance of the variable impedances in other nodes; c) a phase detector receiving the AC power terminal waveform and providing a synchronizing signal having level changes in predetermined time relationship to predetermined points in the AC power terminal waveform; and d) a signal generator receiving the synchronizing signal and providing the output data signal to the control terminal, said output data signal changing levels in predetermined time relationship to the level transitions in the synchronizing signal.