USB ID pin voltage

[gaminn]

Hi,
I'm designing USB device which will control ID pin to tell USB host (tablet) whether the USB host should supply 5V on the bus (ID pin shorted to ground) or whether there is externally supplied 5 V on the bus so the host can charge itself (ID pin connected via xx kOhm resistor to ground).

Is there any specification what voltage will USB host use to sense the ID pin? Is that 5 V or 3V3?

[Renate]

It's generally presumed that what is presented to the ID pin is a pure resistance, in the simplest case open or shorted to ground.
I've seen OTG hosts that use a simple 3.3V GPIO input pin with the SOC pullup resistor.
I've seen OTG hosts that use an ADC and a current source or pullup.
I think that some of those are always on and some of them are pulsed and polled.
Support for random values of ID resistances is varied.
Support for OTG peripherals powering the host is variable too.