Repeater for distributed arbitration digital data buses

A bus switch for exchanging information between digital computing devices respectively connected to a shared or to one of a plurality of sharing distributed arbitration digital data buses, said bus switch interconnecting said shared and a selected one of said sharing data buses into a single composite digital data bus to which composite bus said digital computing devices connect in parallel, said information being exchanged between devices connected to said composite digital data bus in accordance with a protocol having a plurality of phases, said bus switch comprising:

• shared bus interface means, connected to the shared distributed arbitration bus, for receiving signals from and transmitting signals to devices connected to the shared distributed arbitration bus;
• a plurality of sharing bus interface means, each of said sharing bus interface means being respectively connected to one of said sharing distributed arbitration buses, for receiving signals from and transmitting signals to devices connected to the sharing distributed arbitration bus to which said sharing bus interface means connects;
• selection switch means for choosing which one of said sharing bus interface means is enabled for exchanging information between devices respectively connected to the shared bus and the enabled sharing bus;
• and
• control circuit means, simultaneously connected both to said shared bus interface means and to said sharing bus interface means, said control circuit means responding to a plurality of signals on said buses and to the occurrence of a sequence of phases of said bus protocol for controlling the exchange of information between devices connected to said composite bus.

A method for operating a repeater for exchanging information between digital computing devices respectively connected to a first or a second distributed arbitration digital data bus, said distributed arbitration digital data buses being interconnected by said repeater into a single composite digital data bus to which composite bus said digital computing devices connect in parallel, each of said digital data buses employing an identical protocol for exchanging information between pairs of digital computing devices connected thereto, which protocol includes a bus free phase during which none of the devices connected to said bus exchanges signals with any other device connected thereto, said protocol further including an arbitration phase that follows said bus free phase during which a digital computing device connected to said composite bus arbitrates to win control thereof to participate in a subsequent information exchange phase of said protocol, said protocol further including a selection phase that follows said arbitration phase during which a digital computing device that wins control of said composite bus selects another digital computing device with which information will be exchanged during said subsequent information exchange phase of said protocol, said digital data bus including a busy signal that is asserted by a digital computing device to indicate both the beginning of said arbitration phase of said protocol and that the device asserting said busy signal is participating in the arbitration phase and is attempting to win control of said composite bus, said digital data bus also including a plurality of device identification signals that devices, which assert the busy signal which they respectively apply to said first or second bus, selectively assert during said arbitration phase to indicate each device's priority for control of said composite digital data bus in relation to other devices connected to said composite data bus, furthermore, during said selection phase of said protocol said device identification signals being selectively asserted by said device that wins control of said composite digital data bus to identify that digital computing device connected to said composite bus with which said controlling device will exchange information, said digital data bus further including a selection signal that is asserted during said selection phase by the digital computing device that controls said composite bus to indicate that such controlling device is selecting another device connected to said composite bus with which said controlling device will exchange information, during said selection phase said selected device transmitting a signal through said repeater to said winning device acknowledging that it has been selected for information exchange, said repeater receiving signals from and selectively applying signals to both of said digital data buses, said method for operating said repeater comprising the steps of:

• while both said first and said second digital data buses remain in their bus free phases, remaining in a quiescent state in which said repeater asserts none of the signals that it applies to either bus;
• if any device connected to said first or second bus commences said arbitration phase of said protocol by asserting the busy signal of that bus, responding to such assertion of said busy signal by asserting the busy signal of the other bus;
• during said arbitration phase of said protocol, responding to assertion of a device identification signal on said first or second bus by asserting that signal on the other bus;
• upon assertion of said selection signal by said winning device, storing information identifying to which of said first or second buses said winning device connects;
• during said selection phase of said protocol, responding to assertion of said selection signal of said first or second bus by said controlling device by asserting the selection signal of the other bus;
• during said selection phase of said protocol, responding to said controlling device's assertion of a device identification signal on said first or second bus by asserting that identification signal on the other bus;
• and
• upon said selected device acknowledging that it has been selected for information exchange, storing information identifying to which of said first or second buses said selected device connects.