TOMTOM TMC receiver serial data format

grazz · Occasional Visitor Joined: Apr 24, 2007 Posts: 7

Hi,

To start an apology - sorry to cross post i realised that the advanced GPS forum wasn't the right place for this post so i'm reposting it here. Embarassed

I'm trying to determine the TMC serial output from my TOMTOM TMC receiver for my car pc

I've got a standard TMC device from the tomtom 510/710/910 serial, which I've line converted the output from 3v TTL to Serial, on a scope it looks like 19200bps baud (smallest blip was ~52us long = 19200). I was expecting TMC data such as PI code, LocationID, Event ID etc as in the TMC ISO spec but instead I get this sort of data:

0d;0a;00;04;0c;00;1b;00;4f;00;10;0a;80;25;00;2a;e3;0d;0a;
0d;0a;00;04;0c;00;29;00;55;00;10;0a;44;25;00;2a;0f;0d;0a;
0d;0a;00;04;0c;00;22;00;57;00;10;0a;80;25;00;2a;c2;0d;0a;

Anyone know anymore, if this is encoded or the format of this data, i'm wanting the Location code, and Event code from this stream?

Thanks!

Darren · Posted: Tue Apr 24, 2007 8:12 pm Post subject:

Looks to be encoded to me, I assume this is data captured when you had an active TMC reception?
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Darren Griffin

grazz · Occasional Visitor Joined: Apr 24, 2007 Posts: 7

I can't really tell as it is just plugged into the PC, it receives much more data per seond at home than work (the building is steel framed and foil tinted windows which stops GPS and mobiles pretty efficently), so i'd assume this is TMC data in some format.

The data strings always start with 0d,0a and always end with 0d,0a but i can't see anything inbetween that matches TMC data as I know it...

philpugh · Posted: Wed Apr 25, 2007 2:33 pm Post subject:

grazz

Interesting sequences you are getting. 0D 0A would be carriage return, line feed but the majority looks like binary data. But there are a lot of charaters the same repeated in the same position in each string which could indicate the positions of codes, data etc.

Have you tried inverting the signal from the unit - see if you get any more meaningful information?

I would expect the data to be 'encoded' by TomTom as there is no reason why they should use a 'standard' output for a proprietary solution. However you would expect the data you are anticipating to be present in some form.
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Phil

mikealder · Posted: Wed Apr 25, 2007 4:48 pm Post subject:

Have you actually received TMC data on the TomTom unit sat in the building? if its as well screened as you say I doubt it will achieve signal lock to a Classic FM transmitter unless you happen to be sat right next to it.

What you might be seeing is the frequency the unit is trying to tune to as this is repeated durring the tuning scan. As the frequency is displayed on the TomTom unit the RDS unit must output that information.

I doubt the actual data is encripted by TomTom prior to transmission, Navman use the same data from the same RF network, the data will contain start point, end point and incident type for each problem.

Make sure you are actually receiving data when sniffing for data traffic, a PC with two RS232 ports might help with this, then look at both data sets (record them) prior to onward transmission via the second port - bi-directional comms, and you might need the TomTom device connected to get the receiver to kick in fully - Mike

grazz · Occasional Visitor Joined: Apr 24, 2007 Posts: 7

Thanks guys, I've tried the basics by inverting, bit reversing the data, i can't see any c2a1 or similar indicating classic fm for instance.

I'm going to try as you say hooking it to the tomtom unit, but sniffing the comms trafic in both directions on a PC, maybe i will be able to see any setup information from the tomtom unit, or at least if the unit is receiving data. I think it is as its spitting out much more at home.

Its a shame i don't have another receiver with NMEA style TMC data being printed out from the same radio station to compare...

grazz · Occasional Visitor Joined: Apr 24, 2007 Posts: 7

ah ha... getting there, heres some more data...

0d 0a 00 03 0a 00 08 28 00 69 18 d5 0e 2a 83 0d 0a
0d 0a 00 03 0a 00 03 30 00 e2 01 46 cd 2a 52 0d 0a
0d 0a 01 03 04 00 0c 2a 0a 0d 0a
0d 0a 00 03 0a 00 08 28 00 69 18 d5 0e 2a 83 0d 0a
0d 0a 02 03 0b 00 20 20 62 72 6d 62 20 20 2a 15 0d 0a
0d 0a 00 03 0a 00 08 28 00 68 58 a0 0e 2a b7 0d 0a
0d 0a 02 03 0b 00 20 20 62 72 6d 62 20 20 2a 15 0d 0a
0d 0a 00 03 0a 00 08 28 00 68 58 a0 0e 2a b7 0d 0a
0d 0a 00 04 0c 00 34 81 59 00 10 0a a8 25 64 2a 17 0d 0a

note that the 0d 0a 02 03 strings have ascii embedded in them..

[space][space]brbm[space][space]

I.e. my local radio station... damn didn't spot this before!

Also the 0d 0a 00 04 looks like a traffic report

8159 is a location code near me about 4 miles away
0010 or 642a are event codes... one must be right

almost there i think...!

swing · Posted: Wed Apr 25, 2007 9:18 pm Post subject:

One thing you need to understand is that the TMC data feed does not include co-ordinates for the start and the end location. Instead, the data feed simply has a location ID code for the two points - so 8159 may well be a location code. Within the software within TomTom is a location table, which translates this value into a position within the maps.

So, even if you manage to fully decode the content of the message stream, I'm not sure what use it will be...
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lbendlin · Posted: Wed Apr 25, 2007 9:24 pm Post subject:

The TMC data contain the location ID and the direction and extend of the disturbance (like, backup for four locations).

Without the complete location table (including the links between the IDs) this data is not much use. You can get the TMC specification from the OpenTMC.org site.
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philpugh · Posted: Thu Apr 26, 2007 1:56 pm Post subject:

You've probably spotted it but there are several parts to each message

0D OA nn nn (Some sort of message id?)

Next character gives length of next message (eg 0A = 10 chars to follow)

0D 0A as a termination
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Phil

philpugh · Posted: Thu Apr 26, 2007 2:02 pm Post subject:

Also the last two characters of the variable length part are 2A nn

2A = *
nn = Checksum

(As seen in NMEA sentences)
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Phil

grazz · Occasional Visitor Joined: Apr 24, 2007 Posts: 7

Thanks everyone, i have a table of tmc event codes and lcations so the data will be useful once i've figured out where it is in the stream.

Just an update, i've connected the tmc device to the tomtom unit and i'm sniffing the serial data from both devices on my pc. I can see data both ways, the tomtom then configures the receiver to select classic fm to get the tmc data. The tmc data stream is then more consistant, although its not matching up with the event locations table i have.

I think i will try to hook up the PC directly to the tomtom go unit and fake a repeated tmc data location string, and see what the tomtom decodes it as, hopefully that will help out in my decoding...!

swing · Posted: Fri Apr 27, 2007 7:32 am Post subject:

Where did you get the location table from? Is the right table for iTIS, and is it the latest version?
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grazz · Occasional Visitor Joined: Apr 24, 2007 Posts: 7

These ISO documents cover the event and location codes:

ISO 14819-2 Event Coding
ISO 14819-3 Location Coding

philpugh · Posted: Fri May 04, 2007 3:32 pm Post subject:

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