showing bus data on a LCD display

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Dutch
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showing bus data on a LCD display

Post by Dutch »

Hello,

Down in the picture you see a serial signal from a J1850 VPW (variable pulse width) databus.

I have tryed to capture the changing data for investigation with a Fluke 225c scoop from work. unfortunately the datastream is too fast for the maximum recording speed.

there are many different signals and according the data sheet of the signal after negotiation bits the data I want to know is send. this seems to be from the 9th data bit up...

the '1' and '0' in a row is read accordingly.. Start-Of-Frame: Signal high for 200uS ......"1" Bit: Signal low for 128uS or high for 64uS "0" Bit: Signal low for 64uS or high for 128uS
you can see the left first high is indeed the 200uS and than the next 8 changes are not really important for what I want to get out that stream...... from 9 and up need to filter out that data...

I 'think' the data needs to pass a loop where it 'writes' the data after the start... just how do I put something into a memory? or am I seeing this wrong?

Can someone (PLEASE!) tell or point me in the direction how i do that? I'm learning myself into this...

There is a lot of knowledge here, I know.. I have good hope someone on this forum knows this stuff. Who shoots?
Any help is very welcom!
Regards Angelo
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Dutch
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Re: showing bus data on a LCD display

Post by Dutch »

reading and searching a lot to find a solution for my 'J1850 can/data bus reader' I found when i search 'Bus' in the matrix website I get a few hits. http://www.matrixtsl.com/search_results ... chText=bus So it is there! i'm probably thinking too hard about it....does someone know if the CAN macro's used in the examples are suitable for the J1850 VPW can-signal i want to decipher or can the settings be changed to work?
I have a working example of a 14 year old display with a pic 16F87 I believe doing exactly that. so it can be done.

Help... don't have that much time left from my free trial month.. if I have a idea I can get this worked out a bit (with help I have to admit) I have a better feeling paying for flowcode 6 I have put money for aside.
Thanks. appreciate any answer what helps. Angelo.

kersing
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Re: showing bus data on a LCD display

Post by kersing »

Angelo,

J1850 VPW is a vehicle data bus, but it is not CAN. The two are different and using the CAN component will not work.

The simplest solution to interface to the bus would be to use the ELM322. It can be found for sale at this site which has the data sheet as well. Apparently that chip is a PIC of some soft with the protocol implemented in software.

If you want to implement the protocol yourself, you could start with the C sources for AVR at this site or the 'translation' to a PIC controller found here. As the PIC code is for BoostC, the compiler Flowcode uses for PIC controllers, it should not be too difficult to use it in C code blocks.

Best regards,

Jac
“Integrity is doing the right thing, even when no one is watching.”

― C.S. Lewis

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