Hi Allen

            Thanks for your reply but I am bit confused about formula. In the manual the formula mentioned;

     TSeg1 = (TSEG1 + 1)*tq

      TSeg2 = (TSEG2 + 1)*tq

Where   tq = (BRP+1)/fCAN

so

            tq = (15+1) /40000000

                        tq = 0.0000004

                        TSeg1 = (4+1)*tq

                        TSeg2 = (3+1)*tq

Substituting, I get
     Baudrate = 40,000,000 / ((15 + 1) * (1 + (9*tq)))
                   = 40,000,000 / (16 * 1.0000036)
                   = 40,000,000 / 16.0000576
                   = 2499991

Finally the Baudrate is 2499K. Please clarify me where I went wrong.

Personally I am not interested in code generators but since I am new to CAN how do I verify my configurations. Is there any way to verify my register settings other than DAvE? Please let me know.
             

My first thought is that you either hit a typo during the calculation or bounced a "9" during the e-mail; after all, 249,991 is reasonably close to 250,000 and the numbers sometimes aren't exact.  But, in digging into this, I don't see an issue and I can't duplicate your numbers.
 
WARNING: I have never worked with DAvE (and have both a personal and professional dislike for code generators/wizards; YMMV) and I've never worked with the xc164 but I have worked with the C167 and I can read user's manuals.
 
Based on the TwinCAN User's Manual, your interpretations of BRP and TSEG1/2 are correct.  Further, I see from the manual that

     TSeg1 = (TSEG1 + 1)

      TSeg2 = (TSEG2 + 1)
 
So, I apply the calculation for BaudRate:
     Baudrate = fCAN / ((BRP + 1) * (1 + TSeg1 + TSeg2))
 
Substituting, I get
     Baudrate = 40,000,000 / ((15 + 1) * (1 + 4 + 1 + 3 + 1))
                   = 40,000,000 / (16 * 10)
                   = 40,000,000 / 160
                   = 250,000
 
Dead on.
 
If I try to back-calculate the bit timing:
      2499991 = 40,000,000 / X
 
I get X = 16.00005760...
 
I still think you slipped a decimal somewhere (probably on that 40Mhz but maybe not) but even allowing for that, you're off and this calculation is straight-forward enough that you shouldn't have to worry about truncation or rounding errors.
 
So, the numbers you are working with look right and I can't tell you where the calculation went awry.
 
Regards,
Allen Pothoof
  

From: manivannan.d@...
To: canlist@...
Date: Wed, 24 Jun 2009 10:25:50 +0530
Subject: [CANLIST] Reg CAN Baud Rate Config

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