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Unexpected Messages and Pages

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Total Posts: 11

Joined 2017-01-13

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In an attempt to understand ANT+ better I am looking at some log files. I have come across the following, which I cannot find given in the documentation.

1) The Message ID 0xC6 - I cannot find any documentation of the 0xC6 message
The transmission - A 0x4D request for message 0xC6:
[A4][02][4D][00][C6][2D]
the corresponding receive / return of message 0xC6:
[A4][05][C6][89][F4][90][00][00][8A]

I expected to find 0xC6 in section 9.3 of the ANT Message Protocol, but it isn't there. What is 0xC6 and where can I find the documentation?

2) This 0x4E data message is received from the FE-C device and I do not understand two aspects of it:

[A4][14][4E][00][BC][3D][39][00][88][54][5D][01][E0][C5][A7][79][01][10][01][6D][00][00][87][C7]

2a) the first part of this is a 0xBC page and I expected to find it in section 7 of ANT Fitness Equipment document. It is not there, so does this mean 0xBC is a page used "at the discretion of the developer" in line with 7.13.3 in ANT Fitness Equipment document, or what?

2b) this received message (and several other different ones) are 20 bytes long. The length shows 20 and the checksum is correct, so it appears to be a valid message. This and all similar ones are 0x4E channel messages and have a standard page followed by [E0][C5][A7] and then more bytes. This does not tally with the extended message documentation I have found. What is happening here and where is it documented?

Many thanks
     
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Total Posts: 741

Joined 2012-09-14

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Hi,

That broadcast message is interesting, how did you generate these logs and from what FE-C device did that message come from?

1) 0xC6 is a manufacturer specific message so it's undocumented.

2) a) Page 0xBC appears to be an uncompliant data page. Not only does it fall outside the ANT+ FE-C Device Profile, it also does not fall within the manufacturer specific data page range (0xE0-0xFF) which are the only pages which should be used if proprietary data pages are required...

b) This is detailed in section 7.1.1.4 of the ANT Message Protocol and Usage document. Flag 0xE0 indicates that all of the extended message fields have been enabled.

Best regards      
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Total Posts: 11

Joined 2017-01-13

PM

Hi - Replied to this yesterday but for some reason it hasn't saved in the Forum, probably my finger trouble!

Thanks for the response. The lines are from the log file created by the cycling application Zwift working with an Elite turbo. The log file is clearly not a direct output of the ANT+ communications as they have been altered slightly before output. For example: many messages have two zero bytes added after the check sum byte; the Network Keys are all zero'd out to hide them; there appears to be an extra byte in the extended messages; and some that appear to be just wrong. So as the responses are uncompliant, they may only appear in the Zwift log file but not in the ANT communications. Also it's possible that some of the odd lines are corrupted messages, which the log file does its best to represent.

Thanks for the pointer to the extended message documentation. I think I missed this because, although I suspected extended messages, I read that extended messages start with 0x80 in the second paragraph of 7.1.1, and then discounted them as the cause. That'll teach me to read the whole section!

Best regards      
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Total Posts: 1

Joined 2018-03-05

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according to the extended data, the message is from a combined speed & cadence sensor, not FE-C device. Combined speed & cadence sensor doesn't follow the standard ANT+ message definition. The bytes [BC] ... are simply the Combined Bike Speed and Cadence Data Page