Added method to check/retrieve current DTCs

[jimwhitelaw]

No description provided.

[jimwhitelaw]

OK, I can't figure out how to squash all these commits into one change. I think that has to be done when/if the pull request is merged. I have tested this with 2 different ELM devices, 2 different vehicles and an ELM327 emulator and it works fine, but the responses were significantly different from what was documented in the datasheet. I think it would be useful to have some additional testing by others.

[PowerBroker2]

This looks like a big update with a lot of good stuff! Could you give a brief overview of all the changes? I looked through the branch to main diff and it seems like it's mainly adding a DTC checking function(s) and an example plus some whitespace stuff.

Also, I can squash and merge from my end, so there's no prob there.

[PowerBroker2]

I'll go ahead and merge now to make it easier for others to test but I won't tag out a new version until I can get one more person (maybe me?) to test successfully.

Side note - do you have a reliable way of testing if there are no trouble codes to clear?

[jimwhitelaw]

Yes, it just adds one method and an example program for using it. As for testing if there are codes to clear, this code from my example worked for me:

myELM327.monitorStatus(); // Gets the number of current DTC codes present

    if (myELM327.nb_rx_state == ELM_SUCCESS)
    {            
        // We are only interested in the third byte of the response that
        // encodes the MIL status and number of codes present
        milStatus = (myELM327.responseByte_2 & 0x80);
        numCodes = (myELM327.responseByte_2 - 0x80);

I was thinking about adding another example program just for this use case. It is sort of buried in the one for fetching the codes and that would be easier for people to find.