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Thread: Low Speed GMLAN Interface

  1. #21
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    Quote Originally Posted by E85 View Post
    mmm...that is interesting. GM car obviously. Which model/year?
    That's a Saturn ION. The manufacturer year is '06, though I don't know of the top of my head if the model year is '06 or '07.

    One thing interesting is that I can actually see the high voltage state on the wire from time to time with a scope, even with the engine running. For example, if I open the driver door I always see a blip.

    My neighbor has a late model Yukon, I'll try to take a look next weekend if he is around.

    -jjf

  2. #22
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    Quote Originally Posted by jfitzpat View Post
    One thing interesting is that I can actually see the high voltage state on the wire from time to time with a scope, even with the engine running. For example, if I open the driver door I always see a blip.

    -jjf
    This makes some sense to me, in theory at least. What's the first thing that happens when someone returns to their car - opens the door or they use the remote! In either case a wake-up should be sent; easier for a programmer to use just one command than to generate a separate command for engine running conditions. With the engine running power is not a consideration.

    If you have a remote, I'd bet money that the 12V signal is activated as a wake-up to the rest of the vehicle, same with opening any door.

    Are you only using a scope to look at the signal, or do you have a scanner of some sort. If so what one?

  3. #23
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    so this is kind of off-topic, but do you think we can pool our GMLAN knowlege (and by we, I mean those of you who know anything about it, which would currently exclude me) into some documentation of some sort.

    I'm getting a mod'd OBDPro that should be able to talk to GMLAN SW CAN and I'd love to write a provider plugin for nobdy to be able to understand GMLAN stuff.

    Should we start a wiki page?
    Former author of LinuxICE, nghost, nobdy.
    Current author of Automotive Message Broker (AMB).
    Works on Tizen IVI. Does not represent anyone or anything but himself.

  4. #24
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    Quote Originally Posted by tripzero View Post
    so this is kind of off-topic, but do you think we can pool our GMLAN knowlege (and by we, I mean those of you who know anything about it, which would currently exclude me) into some documentation of some sort.

    I'm getting a mod'd OBDPro that should be able to talk to GMLAN SW CAN and I'd love to write a provider plugin for nobdy to be able to understand GMLAN stuff.

    Should we start a wiki page?
    +1 for a wiki page...there seems to be a lot of knowledge here it would be great to put it together and see what gaps need to be "figured out".

  5. #25
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    Quote Originally Posted by Hebe View Post
    This makes some sense to me, in theory at least.
    Me too. Same thinking.

    Quote Originally Posted by Hebe View Post
    Are you only using a scope to look at the signal, or do you have a scanner of some sort. If so what one?
    Both. I have an AU5790 transceiver hooked to an Atmel AVR (8 bit) MPU that just dumps everything. I hooked my scope up because I wondered if there was something wrong with my wakeup condition detector. The Phillips (now NXP) part offers a pair of pins to set the mode to drive the bus, but you're on your own to detect it.

    -jjf

  6. #26
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    Quote Originally Posted by tripzero View Post
    so this is kind of off-topic, but do you think we can pool our GMLAN knowlege (and by we, I mean those of you who know anything about it, which would currently exclude me) into some documentation of some sort.

    I'm getting a mod'd OBDPro that should be able to talk to GMLAN SW CAN and I'd love to write a provider plugin for nobdy to be able to understand GMLAN stuff.

    Should we start a wiki page?
    I think we are all in the same boat. I see no one who has commented yet that has any in-depth personal experience with the Single Wire(SW) GMLAN(CAN). The money is with OBDII, this is not OBDII and has limited application for the general user.

    I will be very interested in Tripzero‘s modified unit and more importantly the software that comes with it.

    Caveat: I have no experience with CAN. I have only been studying the Transceiver data sheets, application notes and anything else I can get my hands upon, as well as to a lesser extent the Controller chip data sheets.

    What I think I have figured out is it is not that complicated for someone who is familiar with microcontrollers – it is just another signal source. The dedicated CAN Transceiver and Controller chips take care of all the unknown and hard to understand physical stuff and data stream for you. This requirement has been written into the industry standard developed by Bosch and is as such required of all Bosch licensees, i.e. the chipmakers. The Controller chips put out standard signals to the microcontrollers; be it SPI, TWI, LIN, RS-232 or the legacy clocked parallel.

    There are some timing issues to consider when designing a whole vehicle’s CAN system(s). However, I believe most of us are only wishing to add a node to receive and occasionally send data.

    What has me concerned is only a small contingent of OBDII software is written to send “user” defined commands out onto the bus. Some examples are Vehicle Spy & ScanXL, in both cases the “Standard” will not as the “Pro” version can. There is most likely good reason for this inability, if every shade tree mechanic were able to send unknown commands to the vehicle I would imagine the vehicle would do a few flips.

    I would have purchased one of the commercial CAN units (note: not OBDII) long ago, but they do not come with any vehicle specific software. The software that comes with them is rudimentary and geared towards the CAN developer as a learning tool. To get more you have to pay $$$$.

    That is all I think I know at this time. This is all very new to me, as I gave up designing electronics in the early 80’s. My reason for researching this is I want to do things with my vehicle that GM does not support. With all the data transmissions within vehicles it makes it very hard to just wire in some relays and switches anymore!

  7. #27
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    Quote Originally Posted by Hebe View Post
    The money is with OBDII, this is not OBDII and has limited application for the general user.
    Not so much even an issue of 'money'. Most things of interest to me personally are on the HS side.

    Quote Originally Posted by Hebe View Post
    What I think I have figured out is it is not that complicated for someone who is familiar with microcontrollers – it is just another signal source.
    The hardware is trivial. The CAN controllers are a lot harder to configure than they seem like they should be, but once you've done one, you can figure them all out in short order.

    Monitoring for something already being broadcast on the bus is generally trivial. All CAN packets have a very specific structure, so the low level protocol is clear.

    Sending something that spoofs another node is generally not too hard. For example, it is trivial to lock and unlock my daughter's doors. But it really depends on the node and the broadcast being spoofed.

    Being a true, integrated GMLAN node, or fully understanding everything flying around the wire. That's not at all trivial, unless you enter a 3rd party agreement with GM. I'm *told* that the specs, proper, are pretty clear.

    Good Luck!
    -jjf

    Edit: One additional note, it is generally easier to use CAN modules which are integrated into the MPU. Microchip, Silicon Labs, Atmel, Renesas, etc. The message slots are generally memory mapped and more readily accessible. External, non parallel devices are slower and a much bigger pain. Speed isn't really an issue on the slow side, but at 500 Kbit, it really is. That's where extra features in an integrated controller really help a modest CPU keep up.

  8. #28
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    maybe one of these?
    http://www.xpresskit.com/product.aspx?productid=320

    it hooks up to the single wire on the obd2 port and it gives you individual wires for door locks, door triggers, immoblizer override, alarm disarm and depending on the vehicle you can do windows up, trunk pop and stuff like that.

    im thinkin a combo of one of these and a fusion brain might do what you want?

  9. #29
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    Quote Originally Posted by YESindeed View Post
    maybe one of these?
    http://www.xpresskit.com/product.aspx?productid=320

    it hooks up to the single wire on the obd2 port and it gives you individual wires for door locks, door triggers, immoblizer override, alarm disarm and depending on the vehicle you can do windows up, trunk pop and stuff like that.

    im thinkin a combo of one of these and a fusion brain might do what you want?
    If door locks were all I wanted, Yes the product line linked above would probably work. However, knowing me as soon as I get into this stuff I will have other questions and desires. That is why I am looking for a low cost device I can initially use to "concept prove" and then if I want learn and design.

    What I can say is: That manufacturer has indeed figured out the SW GMLAN bus as they link and use it for control.

  10. #30
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    Quote Originally Posted by jfitzpat View Post
    Edit: One additional note, it is generally easier to use CAN modules which are integrated into the MPU. Microchip, Silicon Labs, Atmel, Renesas, etc. The message slots are generally memory mapped and more readily accessible. External, non parallel devices are slower and a much bigger pain. Speed isn't really an issue on the slow side, but at 500 Kbit, it really is. That's where extra features in an integrated controller really help a modest CPU keep up.
    Yes. I took apart my Radio and found both the SW GMLAN and the Hi Speed GMLAN transceivers wired directly to the micro-controllers. This of course removed the CAN Controllers from the picture.

    CORRECTION: It wasn't the radio that I found both the High speed and the SW Transceivers in, but the BCM. The radio only has the SW GMLAN.

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