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Method and apparatus for global polling having contention-based address identification

  • US 5,347,515 A
  • Filed: 03/27/1992
  • Issued: 09/13/1994
  • Est. Priority Date: 03/27/1992
  • Status: Expired due to Term
First Claim
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1. A method of global polling in a loop having a plurality of serially addressable devices each having a unique address and being coupled to each other by a pair of wires, in which data is transferred from or to each device by means of a multi-voltage level line signal generated by a central controller, said method comprising:

  • transmitting from said central controller a preamble signal for instituting global polling;

    transmitting from said central controller a plurality of bit intervals corresponding to a number of bits in an address for each device plus a number of bits in a message;

    self-identification by each device in contention for responding to said central controller, where any of said devices in said loop can respond to the poll and where said central controller does not know the addresses of the devices that will respond to the poll prior to the self-identification step, said self-identification step comprising providing a low impedance across output terminals of said device when an address bit is a first logic state and providing a high impedance across said output terminals when an address bit is a second logic state;

    monitoring the voltage level on said loop by each device in contention;

    ceasing said self-identification step by a device if, when said device provides said second logic state at said output terminals, said monitoring step indicates a voltage level corresponding to said first logic state on said loop.

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