Multiple Millisecond Delay Between the Second to Last and Last Frame Sent by NI 9853Hardware: Industrial Communications>>CAN>>NI 9853
Problem: I'm seeing some delay between the second to last and the last frame sent by my NI-9853. Why is this occuring, and what can I do to avoid this behavior? Solution: When transmitting CAN frames from the NI-9853 on one or both ports, there can be a delay between the second to last and last frames on the order of 10-50 ms. The transmit node waits until the frame is transmitted to the module, and not for the frame to actually go onto the bus. Thus, the node returns before the frame is seen on the bus. Once the node returns (frame is still being sent to the module) the SJA1000 controller is reset, and the module is reset to default (configuration tool) settings. Once this is finished, the frame transmission to the module is completed, and the module sends the frame on the CAN bus resulting in a 10-50 ms delay. There are two possible workarounds for this behavior. First, add a delay at the end of the block diagram. This method is not recommended, because the delay must be long enough for all frames to arbitrate for the CAN bus and be transmitted successfully. Given the nature of the CAN bus, it is possible that a frame with a large ID value, will never make it on to the bus because of lower ID’s being transmitted. The second and recommended workaround is to place a Wait on Transmit Complete method after the last transmit (if transmitting on both ports use a method for each port). This way, the last node in the diagram, the Wait on Transmit Complete, will not return until all frames have been acknowledged on the CAN bus. Related Links: KnowledgeBase 4T7CHPBP :NI 9853 and 9852 with CompactRIO FAQ KnowledgeBase 49C5RI5N : Error -1074388479 With the NI-9853 Module for CompactRIO Attachments:
Report Date: 12/02/2005 Last Updated: 03/31/2009 Document ID: 3S1C34JL |
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