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nedb · 03-07-2013, 04:27

(03-04-2013 20:04)davidmbrady Wrote:
(03-04-2013 19:16)Ray Davis Wrote: I am curious what J1587 data you would push down the J1587 bus to change fan speeds? PID 26 is defined for estimated fan speed. I don't believe in any of the testing that I've done that I've seen that PID actively, but I do see that it is one that is marked as "on request", which certainly might explain it.

Hi Ray,

I appreciate the feedback. Sorry, pardon my sloppiness, I don't have the J1587 specification in front of me. What I'd like to do is see what user-defined MIDs and PIDs are available in J1587 and use that space to report fan speed. My LXi has a variable speed fan. For the case of older non-electronic Wanderlodges we'd need to do the same; that is, use the user-defined MID and PID space to report "proprietary" sensor conditions. Do you know if what MIDs/PIDs are available?

A few things I want to follow up on, from the recent discussion with Ray:

Somewhere I've been on the web (maybe in the CANduino pages?) discussed an issue with buffer filters and masks--if I remember correctly what I read, the CAN data stream will overflow the buffers if every message is accepted, so they configure filters and masks to get only the messages of interest, which I think means the CAN bus will have data for only the MIDs/PIDs requested or allowed by the mask/filter. At any rate, it sounds like it can handle many fewer messages than A SAN or CAN is capable of generating.

If filters/masks are a normal part of your DDEC or CAN configuration, then it *could* be where the fan speed PID 026, identified in the spec but not seen in Ray's tests, could be dropping out. Or, maybe a lot of other things--I bring it up to keep it in play, because it kinda suggests that there is a lode of data waiting to be requested or transported. Talk about the benefits of leveraging existing resources Rolleyes

Does VMSPC let you request PIDs that it isn't already reporting? Any front end would have to know something about the requested data in order to display it in a graphical or otherwise sensible way, and I am guessing that adding PIDs/MIDs to the stream means a big fat change request for the GUI developers. Or maybe they've already included a library of gauge parameters for every CAN PID Blush

Did you get a complete list of PIDs/MIDs? The J1587 spec is available on the SAE web for ~$60 download. Angry

Beware, they will try to up-sell you to a subscription to the entire collection of J1939 family of documents. It is all more $$$ than I want to pay--I'm going to beat the bushes some more to see what is freely available. Some CAN books at Amazon look interesting--check the reviews, some aren't as targeted as their titles suggest. But I think I am going to dig around for good web resources. I expect the openCAN spec will reveal a lot.

Have fun. Idea

--Ned

----------------
Ned Bedinger
'91 SP36

A fowl doesn't forget
where the eggs are laid.