Then the circuit board must be powered by the phone since it works without the cable as Fr33dom mentioned.
A microchip would need so small a charge to fire off a signal that perhaps a small capacitor/battery exists to send a signal to the phone to ID the dock. That would explain why when I first plugged the phone into the dock, it didn't respond. The dock hadn't been powered for a couple days since I'm on vacation. I'm still going to cling to the theory of a microchip until otherwise informed, but that doesn't necessarily rule out what has been posited before about something being done over the data lines--which, by the way, has some cred since the dock apparently cannot be used to transmit data. I'll confirm this for myself a little later today. I just like the microchip idea better, but then I only know enough about electrical engineering to get into trouble.
Oh, and since I mentioned vacation, here is a series of shots using my d3 and Hugin to stitch them all together:
Based on the following information, I still believe that the Docking for the Droid 3 is based on electrical reading from the pins of the micro USB connector on the docks. This is why I think it is in this manner.
1. You cannot transfer data when the Droid 3 is docked in either the car dock or the multimedia dock. This is straight from Verizon and I think I saw it on the Multimedia Dock instructions or box. (This shows that at least 1 of the 2 data lines in the USB cable are used for something other than data).
2. The person who modified an OG Droid multimedia dock to use for the Droid 3 used the OG Droid short cable and is able to transfer data to/from his Droid in this dock. His Droid 3 does not recognize that it is docked in this modified OG Droid dock. This also shows that the pin definition is redefined within the short cable.
#1 shows me that the short cables in both the Droid 3's car and multimedia docs are each using one of the two data signal pins, in a proprietary manner, to identify when the Droid 3 is dock and which dock it is in.
#2 demonstrates that this proprietary redefinition/usage of the data lines occurs in the short cable within the dock since any micro-USB cable that meets Motorola specification can be used with the Droid 3 AC charging, auto charging, data transfer/charging, or docking. There are cables that do not meet the Motorola specification, such as those used by the LG ENV3, and some third-party. I have a bunch of these that do not have same pin definition for data, they charge fine the Droid 3 fine, but cannot be used for data transfer.
I have not yet been able to obtain a Droid 3 multimedia dock or short cable that I can take apart and verify the connections.
Just my opinion, most likely your will differ.
I think I can independently confirm this just by reporting that the car dock cable does nothing plugged into my laptop and phone. But plugged into my laptop and car dock it looks like it would charge and it does go into car mode. Of course my earlier findings indicated that the car dock alone will throw the phone into car mode. Whats interesting here is the message about the phone being fully charged that appeared only after attaching the car dock. So the cable is proprietary--perhaps we shouldn't call it USB then. This probably goes allot further toward explaining the inexplicable problems others have had with using non Moto cables connected to their laptop.
I've no idea why this would be true, but everything REMilk says looks quite plausible considering what I've seen so far.
A bit of soapbox standing here. I don't recall USB being used in any sales literature for the d3, but I certainly had the expectation that I wouldn't be beholden to Moto for cables of all things. I also had the expectation that the cables would be interchangeable with my d1 and my wife's phone cable. Although I haven't experienced any issues with using my old d1 cable for charging at work, I am disappointed. Now returning the soapbox for community use.
It's a subtle wiring mod in the Motorola docks that switch the phone into car, media or desktop mode.
Motorola RAZR, RIZR, Z8 mini-USB Charger pinout and wiring @ pinoutsguide.com
Found this while trying to figure out why I get a shock when my VZW DC charger is plugged into my Motorola dock. Don't know if this is the cause yet, but I'm thinking this might be on the trail.