Powering on RMP with USB connected fails

[twlbean]

When I connect the USB line to a hub that is unpowered but connected to running computer, I am unable to power on the RMP. According to the documentation I have, the front lights indicate the processors are in "reset".

I have to unplug the USB, power on the RMP, and then plugin the USB line. This presents a significant problem for our application.

Is there a fix or workaround?

[Craig]

The USB hub is transferring power to the RMP causing the centralized controller to boot. Since the Kill switch is not powered up from the +5V of the USB the machine assumes the kill switch has been pressed.

I believe a potential work around is to remove the +5V line from the USB cable that connects to the platform. Give it a try and let me know how it works.

[phussey]

I just tested Craig's suggestion and it does not work because the +5V line is used by the PC to detect a device.

There is no way (currently) around having to power the machine and then connect via USB with pre-production CCU hardware (rev AA). We will discuss and see if there are any alternatives for customers with pre-production hardware.

[Craig]

I think the only way to make this work is if you supply +12V from an external supply. It may be possible to rig up a DC/DC converter than can power the +12V Disable line from the +5V on the USB. If the DC/DC got its input from the USB power and had its output ground connected to the board ground then the +12V signal could be run through the users kill switch and into pin 3 of J8.

Future revisions of this board will be able to use a +5V signal as the kill switch control so this won't be an issue.