Can interface with enhanced fault confinement

Claim 1

A controller area network (CAN) interface unit comprising a bit stream processor, the bit stream processor announcing when errors are received from a CAN bus; error management logic coupled to the bit stream processor, the error management logic receiving errors announced by the bit stream processor, determining in which of a plurality of error states the CAN interface is operating and informing the bit stream processor of which of a plurality of states the CAN interface is operating, the states including an error active state in which the CAN interface participates in bus communication and transmits a dominant error flag, an error passive state in which the CAN interface participates in bus communication and transmits a recessive error flag, the error active state transitioning to the error passive state when an error count is greater than or equal to a first predetermined number, and a busoff state in which the CAN interface does not participate in CAN bus activity, the error active state transferring control to the busoff state when a count is greater than or equal to a second predetermined number, the second predetermined number being greater than or equal to the first predetermined number, the busoff state transitioning to the error active state using a fault recovery method selected from between a first fault recovery method and a second fault recovery method, the first fault recovery method transitioning to the error active state after receiving a predetermined number of recessive bits by the CAN interface and the second fault recovery method transitioning to the error active state after receiving a predetermined number of good CAN frames, a good CAN frame including an acknowledge delimiter, an end of frame message and an intermission message.

Claim 6

A method of providing a controller area network (CAN) node of a CAN system with a fault recovery feature comprising: setting the CAN node to a busoff state when an error is detected by the CAN node; determining whether to use a first or a second fault recovery method; the first fault recovery method including detecting when a predetermined number of recessive bits have been received by the CAN node; and setting the CAN node to an error active state when the predetermined number of recessive bits have been received by the CAN node; the second fault recovery method including receiving a plurality of CAN frames; detecting when good CAN frames are received by the CAN node; and setting the CAN node to an error active state when a predetermined number of good CAN frames are detected, a good CAN frame including an acknowledge delimiter, an end of frame message and an intermission message; and performing one of the first and second fault recovery methods based upon the determining step.

Claim 7

A method of providing a controller area network (CAN) node of a CAN system with a fault recovery feature comprising: setting the CAN node to a busoff state when an error is detected by the CAN node; determining whether to use a first or a second fault recovery method; the first fault recovery method including detecting when a predetermined number of recessive bits have been received by the CAN node; and setting the CAN node to an error active state when the predetermined number of recessive bits have been received by the CAN node; the second fault recovery method including receiving a plurality of CAN frames; detecting when good CAN frames are received by the CAN node; and setting the CAN node to an error active state when a predetermined number of good CAN frames are detected, a good CAN frame including an acknowledge delimiter, an end of frame message and an intermission message; and performing one of the first and second fault recovery methods based upon the determining step.