System and method for terminating a bus

Abstract

An exemplary system includes a bus (such as CAN bus) having at least two end points. A first and/or a second set of an undetermined number of devices may be connected to the bus. A controller is also connected to the bus, and is configured to establish a termination of the bus at one of the end points relative to the first and second sets of devices, dependent upon whether the controller receives a reply message in response to a communication test message sent to the first and second sets of devices at different times. If the controller discovers that devices are connected to the bus in both sets, the controller is relieved of establishing an end point on either end of the bus. Otherwise, if the controller discovers that devices are only connected to the bus in one of the two sets, the controller is therefore, configured to terminate an end of the bus.

1 . A system comprising: 
 a bus having at least two end points;    first and second sets of devices each containing a quantity of devices from 0 to N, wherein N is any integer greater than 0, and wherein said first and second sets of devices are connected to said bus;    a controller coupled to said bus, configured to discover whether to terminate said bus at one of said end points relative to said first and second sets of devices, dependent upon whether said controller receives a reply message in response to a test message sent to said first and second sets of devices.    
   
   
       2 . The system as recited in  claim 1 , wherein said controller is configured to terminate one end of said bus opposite said first set of devices, if said controller receives a reply message from said first set of devices, but does not receive a reply message from said second set of devices.  
   
   
       3 . The system as recited in  claim 1 , wherein said controller is configured to terminate one end of said bus opposite said second set of devices, if said controller receives a reply message from said second set of devices, but does not receive a reply message from said first set of devices.  
   
   
       4 . The system as recited in  claim 1 , wherein said controller is further configured not to terminate either end of said bus, if said controller receives reply messages from said first and second set devices.  
   
   
       5 . The system as recited in  claim 1 , wherein said controller is configured to (i) deactivate said second set of devices and (ii) enable said first set of devices, when sending a test message to said first set of devices.  
   
   
       6 . The system as recited in  claim 1 , wherein said controller is configured to (i) keep enabled said first set of devices and (ii) enable said second set of devices, when sending a test message to said second set of devices.  
   
   
       7 . The system as recited in  claim 1 , wherein said bus is a CAN bus and said controller is a paper handling controller for a printing device.  
   
   
       8 - 14 . (canceled)  
   
   
       15 . A method of terminating a CAN bus, comprising: 
 enabling a first branch of said CAN bus;    establishing a controller as a termination point on said CAN bus by connecting a termination resistor in parallel with said controller;    determining whether there is a device, other than said controller connected to said first branch, by sending a first communication message on said CAN bus and awaiting a reply message;    if a reply message is received, disconnecting said termination resistor from said controller, thereby removing said controller as said termination point on said first branch;    leaving enabled said first branch of said CAN bus;    enabling a second branch of said CAN bus;    determining whether there is a device, other than said controller connected to said second branch, by sending a second communication message on said CAN bus and awaiting a reply message;    if no reply message is received in response to said second communication message, re-establishing said controller as said termination point on said CAN bus by reconnecting said termination resistor in parallel with said controller.    
   
   
       16 . The method as recited in  claim 15 , wherein said resistor is connected and disconnected by a switch managed by said controller.  
   
   
       17 . The method as recited in  claim 15 , wherein said controller is a paper handling controller.  
   
   
       18 . The method as recited in  claim 15 , wherein said first branch is a portion of said CAN bus with at least one paper handling device coupled thereto.  
   
   
       19 . The method as recited in  claim 15 , wherein said second branch is a portion of said CAN bus with at least one paper handling device coupled thereto.  
   
   
       20 . The method as recited in  claim 15 , further comprising maintaining said controller as a termination point on said CAN bus if no reply message is received in response to said first communication message.