Can interface selecting one of two distinct fault recovery method after counting a predetermined number of recessive bits or good can frames

• US 5,574,848 A
• Filed: 08/24/1993
• Issued: 11/12/1996
• Est. Priority Date: 08/24/1993
• Status: Expired due to Term

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Thomson, Thomas W.
• Primary Examiner(s): Lee, Thomas C.
• Assistant Examiner(s): Chen, Duo
• Application Number:
  US08/111,383
• Time in Patent Office: 1,176 Days
• Field of Search: 395/200, 395/275, 395/500, 371/11.2, 371/29.1
• US Class Current: 714/2
• CPC Class Codes: H04L 12/40013 Details regarding a bus controller
• CPC Class Codes: H04L 2012/40215 Controller Area Network CAN
• CPC Class Codes: H04L 2012/40273 the transportation system being a vehicle
• CPC Class Codes: H04L 49/90 Buffering arrangements
• CPC Class Codes: H04L 49/9068 in the network interface card
• CPC Class Codes: H04L 9/40 Network security protocols

Abstract

A CAN node with a CAN protocol controller device reconnects to a CAN bus from the node'"'"'s busoff state only after the node has successfully decoded a plurality of good messages from other devices on the CAN bus. Reception of a plurality of good messages advantageously provides a CAN protocol controller device which exits its busoff state with a high degree of confidence that the fault that caused the node to enter the busoff state has been cleared.

Claims

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.

2. The CAN interface of claim 1 wherein good frames are determined by detecting end of frame messages.

3. A method of providing a controller area network (CAN) node of a CAN system with an enhanced 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; and

performing one of the first and second fault recovery methods based upon the determining step.

4. The method of claim 3 wherein the second detecting step further comprises

determining when an end of frame signal is received by the CAN node.

5. The method of claim 4 wherein

the end of frame signal includes a plurality of recessive bits and,

the determining step includes counting the plurality of recessive bits.