capture/repeat data ?

[Sam]

Hi,
Is it possible to capture 1 small part of serial data to a pic or eprom ?

I would then like to program the pic to re-transmit it at a different time of my choosing.

Thanks for any advice.

[paul borgmeier]

YES (you haven't given much detail so it is hard to answer in more detail - what are you trying to do?

[Sam]

Thanks Paul,

What I would like to do is to be able to record a part of the data sent in my GM vehicle when, for example, you press window down and be able to repeat that at any time. Such as when I press window down on the driver door, it would also make all the windows go down. This is just an example.

GM uses one data wire running to all modules, when you press passenger window down, it sends data on this wire to the module in the passenger door, this module then activates the window motor. As far as I can determine, the data is called Class II and is sent at approx. 10.4 kbs.

I've hooked my o-scope up to this wire and can see the data sent.

Thank you

[DynamoBen]

It sounds like OBDII VPW.

You may want to think about getting an OBDII to Serial converter and testing with a PC first. I have made several interfaces between these networks and pics. I find it easier to use a converter chip instead of dealing with the protocol myself.

Check out the following for more information.

This company makes the OBDII to serial chips:
www.elmelectronics.com

This company makes assembled units but also publishes pcb's and schematics for personal use:
www.scantool.net

If you want to do it yourself onboard, read the following it talks about VPW and all of its timing requirements:
http://www.circuitcellar.com/adverti...auge%20fuel%22

Let me know if you have more questions.

[Sam]

Hey DynamoBen,

"It sounds like OBDII VPW"

I'm 99% sure that it is.

Thanks alot, I just hooked my old laptop serial input to the vehicle data line and ground (RX to data line and Ground to vehicle ground). I used fogsoft serial recorder to record the unlock and that worked. It recorded a line that appears to be ASCII ???

I'll check out the links you posted. Is it possible to use the laptop to TX this recorded data back to the vehicle's data wire? (Just to see it work)

Thanks again!

[DynamoBen]

If it truly is VPW what you did shouldn't have worked. With VPW pulses are a specific width and occur on either the +7 side or 0. It alternates High Low and the length of time gives you the data bit either 0 or 1. It should not show up as ASCII, although the computer may think it is. What voltage is the line? VPW is around 7V according to the spec. If it is VPW, and I'm 99.9% sure it is, then you would need to have the serial to VPW convert chip that elm makes to transmit and receive messages.

You may also want to check out Serial Device Check, its what I use:
http://www.hackconsulting.com/download.html