On Mon, 14 Jul 2014, Grant wrote: > >> >> You are right, the device will get 5 volts. However it is still part > >> >> of the spec that 2ms without a SOF will force the device into suspend > >> >> mode, so it will use less than 2ma. So depending on your definition of > >> >> function, there will be power, but no activity. If it uses more than > >> >> 2ma, from the bus, problems will ensue. > >> > > >> > What you're saying is true, so long as the spliced USB cable isn't > >> > plugged into a host. But of course, you wouldn't expect to get any > >> > activity on a device when it isn't plugged into a host -- even if you > >> > use a normal cable. > >> > > >> > If the spliced USB cable _is_ plugged into a host then the host will > >> > see it, issue a reset, and start sending SOF packets. In that > >> > situation your comment doesn't apply. > >> > >> > >> I should have been more specific then. I think I understand, but to > >> be sure, if I splice a USB cable, power VBUS with an external 5V power > >> supply, and connect a host and device, the device will work as if the > >> cable was connected to the host normally? > > > > Yes. But why do you want to do this? > > > My application calls for low noise so I'm hoping to feed a clean 5V > from a battery. Okay. Not much you can do about noise on the USB data lines, though. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
