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Answered

jframe input polling question

Zach 9 years ago in IQANdesign • updated by Gustav Widén (System support) 9 years ago • 1
On some machines I have a polling request set for every 500ms.
I wondered how often polling happens by default if I don't use the polling request.

Sometimes I have polling for engine hours, battery voltage, and fuel used.
Sometimes I don't.
I would like to know what to consider for determining when I should.
J1939 is configured for 250kbs.
I have 2 second timeouts.
I thought that the protocol went through each pgn to see if there was information to be exchanged, then it got the information from each pgn.
So if my timeout is 2 seconds, then I would think polling every 500ms would not be something worth doing.
Answered
Gustav Widén (System support) 9 years ago
IQAN will only send out a poll request (using PGN 59904) for the PGN:s where you have defined a poll trigger on your JFIN.

PGN 65253 Engine hours is an example of a PGN that is defined as on-request in J1939, but where I have seen that some engines sends it out also without a request. That may explain why you don't always need to use the poll trigger on your JFIN.


Yes, a 2 second timeout combined with a 500 ms poll trigger is not effective, but that is mainly due to the way that the JFIN handles the timeout. The hint states "If you want to use timeout together with poll trigger, make sure the timeout is shorter than the poll interval, otherwise timeout will not be detected."

The timeout will count from the time you send out the poll request, until the JFIN receives the response.
Sending out a new poll request before the timeout has expired will reset this timer, and you will never detect a timeout on this channel.

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