Wich CAN baudrate is this?

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#1
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Hallo, can someone help me and say me, which CAN baudrate i have with these register values

 

ATMega16M1 with 8 MHz extern oszillator

CANBT1 = 0x12 

CANBT2 = 0x0E

CANBT3 = 0x7F

CANBT1 = 0x12 = Div 9 or 10 res BRP5 BRP4 BRP3 BRP2 BRP1 BRP0 res TQ
  0 0 0 1 0 0 1 0  
CANBT2 = 0x0E res SJW1 SJW0 res PRS2 PRS1 PRS0 res  
  0 0 0 0 1 1 1 0 8
CANBT3 = 0x7F res PHS22 PHS21 PHS20 PHS12 PHS11 PHS10SMP    
  0 1 1 1 1 1 1 1 16

 

8.000.000 / 10 / 24TQ = 33,333 kbit/s

8.000.000 / 10 / 25TQ = 32,0 kbit/s

8.000.000 /  9 /  24TQ = 37,037 kbit/s

8.000.000 /  9 /  25TQ = 35,555 kbit/s

or all wrong?

Last Edited: Mon. Sep 16, 2019 - 10:50 AM
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I would start with using the register setting from the examples in the DS.  Page 240

 

then using a scope or logic analyzer, make your changes as needed to under stand what happens.

Jim

 

 

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Last Edited: Mon. Sep 16, 2019 - 12:46 PM
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Unfortunately, there is no example of my baud rate, so I would like to be able to calculate it myself. I'm already up and down the data sheet, but I'm not behind it

I can watch the data transfer with a DSO a CAN Analyzer from Microchip and a Lawicel Analyzer, but somehow I have an error in it, it will display the ID but no data. That's why I want to start from scratch, not that maybe I have a difference in the data rate.

That's why this cross check would be important for me to what data rate others come.

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kosmos2 wrote:
Unfortunately, there is no example of my baud rate

What baud rate are you wanting?

 

Jim

 

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First of all, I would like to know which baud rate is set at all.

 

I have the problem that my home autmation works reliably, but I would like to access or log on the PC, unfortunately I do not get these loggers set to the same baud rate.

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kosmos2 wrote:
I have the problem that my home autmation works reliably, but I would like to access or log on the PC,

Ok, so your trying to sniff an unknown system.  You will need some basic tools, such as a two channel DSO that you can use to capture the bus states when data is passing.

Another possibility is a logic analyzer.   Do you have either of these available?

Tell us more about your "home automation system", brand, model number, ect.

Are you even sure it is CANbus?

 

 

 

edit: spelling

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Last Edited: Mon. Sep 16, 2019 - 08:48 PM
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It is not an unknown system, because I have developed this myself. Since all my participants work with the same baud rate setting everything works as desired. I only have problems when I hang a foreign participant on the bus.

 

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kosmos2 wrote:
because I have developed this myself.
If you developed it yourself then surely you know what baud rate you set it to operate at ?? I don't understand.

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You seem to have us all confused, start at the beginning and describe the system your attempting to sniff!

You said something about a home automation system, what brand/model number, or if you designed this your self?

We are trying to help, but so far the info provided is confusing and incomplete.

 

Jim

 

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That's why I wanted to start systematically at the beginning, first determine with which baud rate the system should work due to the above settings.

Maybe I just have a baud rate error.

 

At the moment my system only transmits control faults, for example light 1 in bedroom 1 in upper floor = on.

 

I will post a picture of the oscilloscope tonight.

 

I use only these illustrated boards which either query several buttons and then send the command over the bus. Or they are programmed as receivers and switch the desired lamp via a MOSFET

 

 

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So here's the promised image 200μsek / DIV. I have drawn another division 6 bits / 200 μsec.

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Seems like the bit pulses are exactly 200us so it's exactly 5,000 baud

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the gray graduation corresponds to 200 μsec and the red graduation which I drew over about 33 μsec

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It might be clearer if you just show the scope display and the timebase.

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kosmos2 wrote:
which I drew over about 33 μsec

So that works out to about 30303.03 baud

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Which isn't one of the options listed in #1 so I guess it's "all wrong" ;-)