5450404 : Explicit and implicit token media access protocol with multi-level bus arbitration

We claim:

• 1. A method for transmitting a communications medium ownership message between a plurality of transceivers interconnected by a communications medium consisting of a single signal line, said transceivers being peers in that none is a predetermined central bus master, comprising:
  • providing a first jam signal from any one or more of said transceivers onto said communications medium when said communications medium is idle, such that no message other than said first jam signal may exist on the medium;
  • receiving said jam signal at each of said transceivers;
  • providing a second jam signal, from a jamming transceiver onto said communications medium in a time slot associated with a group of transceivers which is less than all of said transceivers and of which said jamming transceiver is a member, which follows the end of said first jam signal by one or more time slots; and
  • transmitting a communications medium ownership message from said jamming transceiver onto said communications medium in a time slot associated with said jamming transceiver, which follows the end of said second jam signal by one or more time slots.
• 2. A method for transmitting a first message between a plurality of transceivers interconnected by a communications medium consisting of a single signal line, said transceivers being peers in that none is a predetermined central bus master, comprising:
  • providing a first jam signal from any one or more of said transceivers onto said communications medium when said communications medium is idle, such that no message other than said first jam signal may exist on the medium;
  • receiving said jam signal at each of said transceivers;
  • providing a second jam signal, from a jamming transceiver onto said communications medium in a time slot associated with a group of transceivers which is less than all of said transceivers and of which said jamming transceiver is a member, which follows the end of said first jam signal by one or more time slots thereby initiating a slot progression for transceivers of said group, for causing the transmission of messages by different transceivers of said group to occur at different times so that collision of messages transmitted by different transceivers of said group is thereby avoided; and
  • transmitting said first message in a time slot associated with said jamming transceiver, which follows the end of said second jam signal by one or more time slots.
• 3. The method of claim 2, further comprising, at the end of the transmission of said first message, each transceiver becoming idle.
• 4. The method of claim 2, further comprising:
  • transmitting a second message following a number of time slots beyond the end of said first message, wherein said second message is a dummy message for preventing the bus from going idle if no other messages are available for transmission.
• 5. The method of claim 2, further comprising:
  • transmitting a second message following a number of time slots beyond the end of said first message, allowing said transceiver to become idle if no second message is available for transmission.