Switch for distributed arbitration digital data buses

Abstract

A repeater ( 40 ) for Small Computer System Interface (“SCSI”) buses ( 52, 54, 56 , and 58 ) to which digital computing devices ( 62, 64, 66, 68, 72 and 74 ) connect in parallel. The repeater ( 40 ) includes a plurality of bus interface circuits ( 48 ) that are connected to the SCSI buses ( 52, 54, 56 and 58 ) for receiving signals from and transmitting signals to devices ( 62, 64, 66, 68, 72 and 74 ) connected thereto. The bus interface circuits ( 48 ) connect to a control circuit ( 44 ), that responds to various phases of the SCSI bus protocol: 1. which stores information for use during a subsequent phase of the SCSI bus protocol; and 2. thereby allows signals to be exchanged between pairs of the SCSI buses ( 52, 54, 56 and 58 ) during a succession of bus phases occurring on the buses ( 52, 54, 56 or 58 ).

1 - 32 . (canceled)  
   
   
       33 . A method for operating a repeater for exchanging information between: 
 i. a first digital computing device directly connected to a first distributed arbitration digital data bus; and    ii. A chosen digital computing device directly connected to a chosen distributed arbitration digital data bus selected from a group consisting of: 
 a. a second digital computing device directly connected to a second distributed arbitration digital data bus; and  
 b. a third digital computing device directly connected to a third distributed arbitration digital data bus;  
   said first distributed arbitration digital data bus and said chosen distributed arbitration digital data buses being interconnected by said repeater into a single, composite distributed arbitration digital data bus;    the first and the chosen digital computing devices connecting in parallel respectively to said first and to said chosen distributed arbitration digital data buses, and to said composite distributed arbitration digital data bus;    said first and said chosen distributed arbitration digital data buses individually, and when joined together by said repeater into said composite distributed arbitration digital data bus, 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 digital computing devices connected to said distributed arbitration digital data bus exchanges a signal with any other digital computing device connected there to;  
 said protocol further including an arbitration phase, that follows said bus free phase, during which a digital computing device connected to said distributed arbitration digital data bus arbitrates to acquire, for an interval of time, a status of a winning digital computing device, and to thereby become entitled to participate in a subsequent information exchange phase of said protocol;  
   said first and said chosen distributed arbitration digital data buses individually, and when joined together by said repeater into said composite distributed arbitration digital data bus, including: 
 a busy signal that is asserted by a digital computing device connected to said distributed arbitration digital data bus to indicate a beginning for said arbitration phase of said protocol, and that the digital computing device asserting the busy signal both is participating in said arbitration phase of said protocol, and is attempting to become the winning digital computing device on said distributed arbitration digital data bus;  
 said distributed arbitration digital data bus also including a plurality of device identification signals that a digital computing device participating in said arbitration phase of said protocol selectively asserts during said arbitration phase of said protocol, concurrently with assertion of the busy signal by such digital computing device, to indicate a priority which such digital computing device has been assigned for use by such digital computing device in arbitrating to win control of said distributed arbitration digital data bus;  
   said repeater receiving signals from and selectively applying signals both to said first distributed arbitration digital data bus, and to said chosen distributed arbitration digital data buses included in composite distributed arbitration digital data bus; said method for operating said repeater comprising the steps of: 
 while both said of said buses forming said composite distributed arbitration digital data bus remain in their bus free phases of said protocol, remaining in a quiescent state in which said repeater asserts none of the signals that said repeater can apply either to said first or to said chosen distributed arbitration digital data buses;  
 if said first digital computing device initiates said arbitration phase of said protocol by asserting the busy signal on said first distributed arbitration digital data bus, responding to such assertion of the busy signal by asserting the busy signal on the chosen distributed arbitration digital data bus included in said composite distributed arbitration digital data bus; and  
   during said arbitration phase of said protocol, responding to assertion of a device identification signal on said first distributed arbitration digital data bus by asserting that same device identification signal on the chosen distributed arbitration digital data bus included in said composite distributed arbitration digital data bus.    
   
   
       34 . The method for operating a repeater of  claim 33  wherein said protocol further includes: 
 a selection phase, that follows said arbitration phase, during which the winning digital computing device selects a particular digital computing device with which the winning digital computer device will exchange information during said subsequent information exchange phase of said protocol;    furthermore, during said selection phase of said protocol one of the device identification signals is selectively asserted by the winning digital computing device to identify the particular digital computing device connected to said composite distributed arbitration digital data bus with which the winning digital computing device will exchange information;    said distributed arbitration digital data bus further including a selection signal that is asserted during said selection phase of said protocol by the winning digital computing device, concurrently with assertion of the device identification signal by the winning digital computing device, to indicate that such winning digital computing device is selecting the particular digital computing device for an exchange of information;    during said selection phase of said protocol the particular digital computing device transmitting a signal to the winning digital computing device acknowledging that the particular digital computing device has been selected for information exchange;    upon assertion of the selection signal by the winning digital computing device, said repeater storing for use in a subsequent phase of said protocol information identifying to which of said digital data buses forming said composite distributed arbitration digital data bus the winning digital computing device directly connects;    during said selection phase of said protocol, responding to assertion of the selection signal on one of said digital data buses forming said composite distributed arbitration digital data bus to which the winning digital computing device directly connects by asserting the selection signal on the one of said digital data buses forming said composite distributed arbitration digital data bus to which said winning digital computing device does not directly connect;    during said selection phase of said protocol, also responding to the winning digital computing device's assertion of the device identification signal on one of said digital data buses forming said composite distributed arbitration digital data bus to which said winning digital computing device directly connects by asserting that identification signal on the one of said digital data buses forming said composite distributed arbitration digital data bus to which said winning digital computing device does not directly connect; and    upon the particular digital computing device transmitting a signal acknowledging that it has been selected for information exchange, said repeater storing for use in a subsequent phase of said protocol information identifying to which one of said digital data buses forming said composite distributed arbitration digital data bus the particular digital computing device directly connects.