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CAN bus sniffing

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Hi All.

I have wired a motec display c125 to a vehicle can bus and have a Bus analyzer connected on the bus also.

Bus speed 500k

11 bit

Sniffed out the Throttle position, coolant temp and engine speed.

My problem is with the engine speed.

The data is using two bytes on byte 4&5

At 800 rpm byte 4 reaches 255 decimal and byte 5 = zero.

Over 800 rpm byte 5 increase by 1 and byte 4 retuns to zero and increases until rpm reaches 1600rpm byte 5 then increase to 2 and byte 4 returns to zero and so on till redline.

In a nutshell byte 4 keeps increasing from 0 til 255 decimal every 800rpm and byte 5 increases by 1 for every 800rpm.

How do i go about in getting the display to interpret the information as rpm?


What ECU are you connecting it to?

The RPM signal is going to be a 16bit number, so you have to read them both together to get the correct speed into the C125. This would likely be a message of Offset 4, Length 2, Bitmask FFFF, Not Signed, Multiplier 1, Divisor 6, Adder 0.

The ecu is a Nissan Hitachi stock ecu.

The offset 3, length 2, bitmask FFFF, not signed. This is the setting i have.

I will try offset 4.


Just an update. I tried offset 4 and it didn't work.

It works now but i had to create a math channel in the display to get the data correct.

Did you try changing the alignment between Normal and Word Swap? this changes the order in which the bytes are read.

No I haven't. But i will try it out.

Thanks for the help.

Black Rex.

Tried the word swap. Works like a charm.

Thanks for the Help.