pcmhacking.net

antus wrote:I know you have looked closely at the data in development of the obd xpro, but Im skeptical of this as the DLC is in hardware. I think the P04 DLC might have less buffer, though, and the later ones have fixed this. P04s are a bit crap in every way, to me they have the feel of being a beta quality design compared to the later ones. Lots of rough edges. For a P01/P59 Ive never seen this due to the operating system. Its always the interface, wiring or power (or a faulty pcm, though Ive never seen that 1st hand as they are pretty reliable)

I do agree that in the 99.99% of cases, it certainly is wiring/noise. Crappy power supplies and poor groundings are accidents waiting to happen.
But after dealing with the P04, I have noticed specific operating systems are not as tolerant, or send frames at crappy timings. In fact, my specific P04 is so unbelievably crap, that we have to add a resistor to the VPW line to help suppress noise. This was reproduced by Pete writing my ecus OS to his P04 and the exact same issues occurring. So far other ECUs have not been that bad, but it just opens the world of possibilities that timings are affected by the OS which is why having the ability to read/write at 1x has become important, since their may be other ecus with the same problem. I could only think that there are specific interrupt routines that are firing off (even when running a kernel) which are causing the undesired delays when writing data from ecu to the scantool.

FriskyDingo wrote:Does the nano draw any power from the obd port? Have you measured it?

I can state that the nano will run (connect to software and lights all function) without power at the obd port
which had blown fuse and thus no communication. When I installed new fuse without disconnecting nano from obd port, I had problems where I had to disconnect nano from PC and restart software in order to get it to communicate. So it needs power at port when it first gets connected, before it attempts communication, or it hangs in some way.

Looking at the nano it says right on it, that it draws 1 Amp.

That seems high, I suspect they might have a safety margin built in to their spec, which is fine to document and make sure people use good enough bench supplies, but I'd be surprised if the nano used that much full time when its running. It sounds like the ecm power + extra draw while it is flashing + interface power + safety margin. Ive seen everything on my bench use 500-700ma during a flash and no significant change to that power requirement with any of the supported interfaces.