TMS320F28069F: Some bytes of CAN bus identifier for extended frame format disappear

Hao Qin

Part Number: TMS320F28069F

Hello,

I use 29 bit identifier for CAN extended frame format. But in canAnalyzer, it only shows 24 bit identifier. For example, I set the identifier is 0x18ff51020, But in canAnalyzer, it only shows the identifier as ff51020. Why does the first two significant bytes disappear? Does any register control these bytes appearing or not? if so, how can I change the setting of the register?

Thanks,

Hao

over 5 years ago

0 Hareesh Janakiraman over 5 years ago

TI__Guru* 95315 points

Hao,

The MSGID is either 11-bit or 29-bits. It cannot be something in-between. If you probe the CANTX pin with an oscilloscope, I am sure you will see all 29-bits. Please see sample waveforms in my app.note at http://www.ti.com/lit/sprace5 . Helpful debug tips in my app.note at http://www.ti.com/lit/spra876 . Please attach a screen capture of your CAN analyzer window showing the truncated MSGID.

0 Hao Qin over 5 years ago in reply to Hareesh Janakiraman

Intellectual 760 points

Hareesh J,

I attach a screenshot of the canAanalyzer showing the truncated MSGID. The identifier should be 18ff51020 but truncated to ff51020. Can you let me know what is the reason?

Thanks,

Hao

0 Hareesh Janakiraman over 5 years ago in reply to Hao Qin

TI__Guru* 95315 points

Did you try increasing the width of that column? Can you probe CANTX pin with an oscilloscope?

0 Joe Josn over 5 years ago in reply to Hareesh Janakiraman

Intellectual 680 points

Please re-check the ID you are trying to TX (1 8f f5 10 20) needs 33 bits.

Truncated to 29 bits is what you get (f f5 10 20)

0 Hareesh Janakiraman over 5 years ago in reply to Joe Josn

TI__Guru* 95315 points

Joe's observation is correct. I missed that point. Thanks Joe.

Only bits 28 to 0 are the MSGID fields. Bits 31, 30 & 29 have other functions.

0 Hao Qin over 5 years ago in reply to Hareesh Janakiraman

Intellectual 760 points

Thanks all for your information.

For Bits 31, 30 & 29, I need set up the them as 1s not 0s for the ID 18ff5102. If I set up MSGID as 18ff5102, the canAnalyzer was shown as 63F as below:

If I set up MSGID as f8ff5102, the canAnalyzer was shown as 18ff5102 as below:

Can you let me know why it happens?

0 Hareesh Janakiraman over 5 years ago in reply to Hao Qin

TI__Guru* 95315 points

Update: Edited my post, since I had mis-typed the bit-position of the IDE bit earlier.

For 29-bit identifiers, the IDE bit (bit 31 of MSGID register) must be 1. If it is a 0, only a 11-bit identifier will be transmitted. i.e. bits 28:18 of MSGID register. Please examine the value of bit 31 in the register window.

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TMS320F28069F: Some bytes of CAN bus identifier for extended frame format disappear