To overcome the 12v signal, Some simple work with transistors would be needed for reading, or voltage divider to bring it down to slightly under 5v for safety. I dont think there is really any need, or ability to TX on VN/VP. Since they output a diagnostic message every 1200ms (something like that). Not a whole heap of great information comes from it either. So the whole TX part can be left completely out.Exactly. Unless the ALDL cable has been specifically designed for 12V signal levels, at the very best, you'd be injecting current into the static protection diodes of the UART-USB bridge chip's RX input via some series resistor, potentially overstressing it and even your PC. You'd better check with the vendor first to see it is safe to do this.
The other risk, which is easily overlooked (even by the vendor), is that the transistor on the TX part of the circuit will not be designed to drive the surge (cold) current of the CEL bulb. So if you accidentally run software that tries to transmit to the ALDL, you'll likely blow the TX circuitry, which may then impact on the RX circuitry (since they are tied together on a common data line), so the whole thing then doesn't work.
A purpose-designed ALDL cable for VN/VP will be designed for 12V signal levels and won't have TX circuitry to blow up. (At the moment, I'm considering designing and making such a cable to sell on eBay, but I'm not sure if there's enough demand to justify the effort.)
But due to this fact that there is next to no good information to pull out of the VN commodores, It doesnt seem there is many people that even want a diagnostic cable. Can see the data below that a VN outputs.. its really not much at all!
All newer commodores have multiple modules that can have information requested or even programmed.
Iv got a prototype on the bench currently waiting to be tested for the VN/VP. Just waiting for the VN ecu I purchased (almost 2weeks ago now.. *sigh*) to rock up for testing and designing up-to-date software for viewing the data rather than the old school winaldl application.