Y-cable and USB-OTG: mutually exclusive / the four connectivity solutions
andy at openmoko.com
Thu May 1 12:40:01 CEST 2008
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Somebody in the thread at some point said:
| Andy Green wrote:
|> This is for the 500mA question? Dunno yet, there can be pins on FTDI
|> that change state under this circumstance.
| There is :) Pin 41, PWREN# (nPWREN in Openmoko terminology).
But I have been reading the pcf50633 datasheet and we have to take a lot
of care about this. Although there is a USB -> SYS programmable current
limit, there isn't one for adapter -> SYS. We have only two handles to
use on this path
~ - dynamically claim adapter power is not present under MSP430 control
(we decide this externally anyway), so pcf50633 will not enable the
adapter -> SYS FET at all until we know we are good for <=500mA
~ - set charging current to zero
What we can't do is set current limit from adapter as we can on USB. We
cannot actually treat it as a second USB interface for pcf50633 purposes
as it is I think.
|> I have a scheme for
|> detecting charger insertion though and that is what is critical.
| Ah, that sounds interesting. Have you figured out a way to detect
| shorted D+/D- ?
Yes I have a plan I will post about. BTW I saw while looking at it that
it seems D- USB pin on GTA02 is floating when GTA02 charger is connected.
|> | to have a only 'dumb power' and 'jtag' port would be somehow
|> | point. especially when its behind a flap with screws.
|> That's what we try to clear up...
| In use cases where you need external power while on the go with USB,
| you probably wouldn't want to have to disassemble your Neo all the
| time. E.g., I think "backup to external storage" would be a plausible
| use case.
| Also, how could an "internal" receptacle be placed such that no crazy
| mechanics are needed and the plug doesn't interfere with anything
| else ?
I imagined if the USB socket is like this (B=battery)
we could mate to it (c = cable)
but I agree external access will be more certain and better and waste
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