Data Format Breakdown/Example

[sirpatrick]

Hello Graham, I really like your app since it allows a person to customize PID's etc. with tags and a nice way to test formulas. Please keep up the excellent work! I am very new to OBD as I have never interfaced with it before. I understand what can be done when one becomes familiar with it. I just received my Vgate Scan OBD-II bluetooth interface and it works as far as I can tell. I have a Hybrid 2011 Lexus RX 450h AWD that I would like to extract all the data I can from it. I like how you have been able to pull data from a prius. I have poked around your app as much as I can and I've been reading up on PID's and other helpful information. It looks like the real data extraction is in the physical addressing rather than just a mode and a PID. If only it was that simple and all the information I needed was in PID's.

My real questions are as follows:
Can you provide descriptions of the address data format breakdown for example:
Address/ID = 7E2

Mode/PID = 21C3

Also, what exactly is response count with a value of 6 with 1000ms. I understand that 1000ms is 1 second between requests for data. I don't want to assume what response counts are.

I am trying to understand what is meant by a formula with an input tag of say "PriusHSD21CEInput{4}" {5}, {6}, {7} and so on for HVBattVolt01, 02 and so on. What are the numbers inside the {?}? Are these more specific addresses? I would like to find out everything there is to know about the data so that I can implement it in my hybrid. I understand what mode 1 and the other modes are but is mode 21 specific to Toyota for the hybrid system? I'm hoping that I can apply any data that you may have so that I can tap into my car. I wish someone came up with an app that was like the scangauge2. Please give any help you can and or databases you might have. It's an honor to be the second person posting in your forum.

Thank you,

Patrick

[Graham Mackenzie]

Hi Patrick, I'll try to answer your questions as best I can. When I started writing the app I had no idea about OBD - I only realised how complicated it can get once I'd started!

Address/ID is the physical address of a particular ECU on the car's network. On a car with a CAN bus (like the Prius) these addresses are like 7E0, 7E1, 7E2. Addressing is done by setting a header in the request when it is sent, CANdroid will set the header if physical addressing is turned on and an address is provided.

Requests can be broadcast to all ECUs - this is functional addressing, and most of the simplest OBD requests are achieved using functional addressing - the OBD adapter takes care of the addressing for these simple requests, all the user has to do is provide the Mode and PID. But on the Prius, at least, some of the more interesting requests can only be made by knowing the correct address and setting the header.

Mode 21 is specific to Toyota (and maybe Lexus I presume?) but I can't profess to knowing what it means.

The response count is more awkward. Most of the simple generic OBD requests (like revs, and coolant temp) reply with only 1 'frame' of data, but some of the Prius specific requests reply with 5 or 6 (each 'frame' can contain 4 pairs of characters). When CANdroid makes a request for one of these it helps to know how my response frames to wait for. If you put 0, it will just wait until it times out, which works fine but this can slow things down when doing many requests per second. If you know that there will be exactly 6 response frames, then you can tell the adapter to wait for 6 responses, then stop and make the next request, speeding things up.

The formulas are a bit arcane, and I've never properly documented them...

Each 'Input' when it runs, makes a request via the adapter, for example for the MAF value we send 0110. I've called this input 'MAFInput'. This returns 2 sets of 2 characters, which might be something like 1D and 60. These are hexadecimal numbers.

Now the formula to calculate the actual MAF value from these numbers for MAF is:

((A*256)+B) / 100

which you can get from en.wikipedia.org/wiki/OBD-II_PIDs

So we substitute 1D and 60 into the formula to get ((1D*256)+60) / 100 = 68g/sec

The way you put formulae into CANdroid is to substitute the Input name and the index of the pair of characters, so for MAF it is

(([MAFInput{1}*256])+[MAFInput{2}]) / 100

I used numbers instead of letters - so A={1} B={2} and so on

So the square brackets [] signify an Input and the curly brackets {} signify the index into the characters in the response.

It does make the formulae look far more awful than just ((A*256)+B) / 100, but it does mean you can combine different inputs into a single formula.

Incidently you can also include Variables into a formula using angle brackets <>.

There is bit of a walk-though here which may help:

candroid.wikidot.com/creating-a-custom-widget-variable-input

Its quite hard to find enough OBD info in one place. I learned mostly from the ELM 327 guide (the OBD adapter chip):

elmelectronics.com/DSheets/ELM327DS.pdf

The Prius specific calls are very well listed in a spreadsheet here:

priuschat.com/forums/gen-ii-prius-technical-discussion/95370-gen2-prius-custom-pids-torque-android-app-formulas.html

Hope I've been some use, let me know if I can explain anything better/more!

Graham