Variable length backplane bus

DETAILED DESCRIPTION The present invention solves these and other problems by providing a backplane bus that can serve a varying number of bus groups.
The bus and the number of bus groups served per backplane can be easily reconfigured in the field as the needs of the system user change.
As before, the backplane bus of the invention interconnects pins on the connectors mounted on the backplane and, in turn, the circuit boards plugged into these connectors.
However, the subject backplane bus is not merely the conductive trace on the backplane interconnecting the backplane connectors.
The bus also comprises circuitry on the circuit boards served by and plugged into backplane connectors.
The boards that are plugged into the backplane are of a first and a second type.
Boards of the first type extend the backplane bus between adjacent connectors.
A board of the second type terminates the bus and does not extend it between adjacent connectors.
This second type of board is referred herein to as an interface/termination board.
A backplane bus group comprises one or more printed circuit boards of the first type together with a single interface/termination board.
The serial chain of connections that make up the backplane bus using the first type of boards is broken by inserting an interface/termination board into the appropriate connector.
A circuit board of the first type installed in the next adjacent connector begins the next backplane bus group on the same backplane.
Thus, more than one bus group can be served on a single backplane without modification of or damage to the backplane bus.
The backplane bus groups can be subsequently reconfigured merely by rearranging, adding or subtracting circuit boards of the first type and by inserting an interface/termination board in the appropriate connectors to terminate each newly formed bus group.
It is not a disadvantage that one circuit board per bus group (the interface/termination board) must be wired differently from the others.
This is true because there is ordinarily a circuit board in each backplane bus group that is unique in other ways