Clarion CeNET – a first glance

I’m keen on reverse engineering at least some aspects of the Clarion CeNET bus in order to hook other gadgets to my car stereo. CeNET is a proprietary interconnect used by Clarion on many of their car audio products over the last ten years.

It uses a proprietary 13-pin square DIN style connector that is not available off the shelf. The pinout is shown below (this was taken from a Clarion service manual).

Electrically, CeNET appears to be a form of asymmetric serial bus. There is some discussion online that suggests a 38400 baud rate. The same person also says that it appears to use some form of encryption which may make it difficult to hack.

My experience with CeNET stereos is that the display will flash SYS or SYSTEM if the battery is disconnected or a CeNET device is inserted or removed. They do this until the stereo is powered on. Perhaps an encryption key is negotiated during that period?

On the hardware side, closer inspection reveals the bus consists of a transceiver IC (CA0008AM) connected to one of UARTs in the host devices microprocessor as shown in the simplified diagram below. Note that there are also some pull-down resistors on the Tx and Rx pins, as well as a 68 Ohm termination resistor across the Bus+ and Bus- pins. I’m unable to find data on the bus transceiver but I guess it’s possible that other generic ICs could be used here. The bus itself floats at 2.5v and swings +/- 200mV during signalling.

I have capture some data samples from a stereo connected to a EA-1251B iPod adapter that emulates a 6 disc changer. I haven’t yet studied them in detail but you can download the capture files below.

You will need to download Saleae Logic to view the capture files (it’s free). The cables were connected according to the colours in the diagram below:

In all captures I powered on the stereo from cold (no battery) immediately, then switched the unit on after about 3 flashes on the display (4-5 seconds). With the EA-1251 samples I switched from radio to the CD changer at about 7-9 seconds. From here the stereo waits for the iPod to wake up (it thinks the CD changer is loading) before it starts playing the first track of the first ‘disc’ (playlist) at about 14-15 seconds. The song then continues to play until the end of the capture.

Update: I’ve also grabbed a couple of samples of a TV tuner and display.

When the TV tuner is selected via the TV display it places the head unit into aux mode (it displays Aux on the screen). This could be a very useful hack; to make a ‘proper’ CeNet aux input. In the samples above, all units were powered up from cold (no battery) immediately after beginning the capture. The head unit is switched on at about 4 seconds, then there is a bit of wait for the display unit to boot up. Once this is done I’ve switched to the TV tuner at about 27 seconds. Shortly after (about 35 seconds) I switch back to the head unit’s internal FM radio.

It turns out trying to capture the bus pins was a waste of time as they normally float at 2.5V. I haven’t been able to look into that side of things any further as my only oscilliscope died before I could check it.

Hopefully somebody else finds this useful. I’ll keep working on it as I get time, and post any updates to the site if i come up with anything.

9 Responses to Clarion CeNET – a first glance

  1. pcedric says:

    Nice to see such technical research about the ce-net. I have such devices here and would like to understand this bus deeply since many year, but I don’t allowed time to do it. Could we get in private contact to push the research ahead ?

  2. Kevin McFarland says:

    I read your article with great interest when I noticed it was for a newer unit. I want to replace my outback factory with the mcintosh, is everything the same?
    I am working on an 01 outback LLBean
    I have a lot of high end equipment but a complete install is very time consuming, from the comments I’ve read the factory Mac unit may not compare to complete renovation of sound system, for a reasonable price you can get decent sound.
    My aftermarket equipment 2 butler tube (reworked) amps with line/speaker level XLR preamp converter. 9 band R/L Zapco EQ.Set 6.5 Diamonds, set 6.5 Boston Pros the pros had the crossover reworked. a 10″ single diamond sub in custom enclosure. and Phillips HU w/changer
    Thanks Kevin

    • nzlamb says:

      The McIntosh is pretty good for factory but retrofitting into a car without it is a lot of work. You need to obtain the amp and plugs, and a set of speakers including the subwoofer and its mount. You will end up removing the front right seat, entire RH boot wall, plus both the kick panels in the front door openings.

      The existing speakers must be rewired to the amp on the floor and you will need to run a power feed to the correct point under the dash (non McIntosh cars still have the power feed ready to wire to). All speakers and tweeters must be replaced with the McIntosh versions which are 8 ohm. You also need to run the audio cable from the HU to the amp.

      If you can get the McIntosh parts for a good price and are not worried about time then it’s worth while. Otherwise you will get better sound from a good aftermarket install with about the same level of effort.

  3. Michael says:

    Hi

    I’m not sure if you’re still checking this but I’m gonna post anyway!!!

    I have seen your posts here and on clubsub about Clarion stereos in Subaru’s. I have got a 2002 legacy GT30 with a clarion CD player and Minidisc (PF-4048I-B) (non-McIntosh). It has got both the CeNet and the 13 pin plugs in the back but it doesn’t have any CD changer controls (found that out the hard way!!!). Apparently, the GPS/tv/air con display draws its power from the headunit via the CeNet plug. This is a problem as I want to swap out the factory headunit.

    My question is, if I hack up the CeNet plug and wire the power, acc power and ground wires per your diagram above, will the air con display work properly? or, are there some other Cenet signals required too?

    Thanks
    Michael

    • nzlamb says:

      That’s a good question! I can check with a unit I have a home when I get back in a week or so. Otherwise see my old post on ClubSub on replacing the satnav with a proper climate panel – http://www.clubsub.org.nz/forum/index.php?topic=4654.0

      • Michael says:

        Hi again

        Have you had a look at this?

        I have tried to bypass the power, acc power and ground wires per the above diagram, but the air con display doesn’t respond at all. Interestingly, when I tested the acc power pin, it didn’t register any current. The constant power and the ground appear to be right though.

        Any ideas on how I can bypass the Cenet connection from the factory HU?

        Thanks

    • Andrey_Rus says:

      Hello! also I have subaru legacy bh5. was able to turn the screen on the navigation device without a head, but that the error did not go away even when you connect the head unit.

  4. Kawal says:

    Looks like the CeNet bus is an IEBus implementation. Ca0008 looks very much like the HA12187FP bus driver. Decoding the bus directly is impossible due tot he differential nature of the bus. You need one of the buffers to decode the bus.

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