Tests on Y-cables

DING Changchang archang at canaan-creative.com
Fri Jan 9 02:17:48 UTC 2015

Werner Almesberger wrote:
> DING Changchang wrote:
>> I have tested two Y-cables Xiangfu bought:
>> http://downloads.qi-hardware.com/people/xiangfu/anelok/y-cable/Y-cable.JPG
>> http://downloads.qi-hardware.com/people/xiangfu/anelok/y-cable/Y-cable-with-chip.JPG
> Great, thanks !
>> They both have the ID pin connected to GND in USB Micro B port as
>> the OTG host.
> I love it ! As far as I can tell, it's totally against anything the
> USB standards define, but it's just what works best for us :-)
>> The first one should meet all the needs:
>> Works fine when connecting usb keyboard/mouse/disk on the OTG slave
>> (the standard USB A female)
> Perfect !
>> The power branch does deliver power to both slave and host, only
>> failing in charging a Nexus5. But it can charge a Nexus4 and power
>> up a RaspberryPi.
> Excellent ! I think the reason that it sometimes works and sometimes
> not is that some systems only draw power when something on the other
> end of the cable tells them it's okay to do so (e.g., when they can
> enumerate), while others just assume they can do it and go ahead.
> The ones that try to be "nice" therefore don't charge / power while
> the ones that don't pay attention to such things will just work.
> USB OTG also specifies three more protocols (ADP, HNP, and SRP) that
> can make life interesting. In particular, ADP (Attach Detection
> Protocol) communicates over VBUS. So it would even work between the
> power-only port and devices on the other ports. I guess that could
> add an extra bit of unpredictability, too.
>> One problem is that the power branch has a Micro B female and is not
>> long enough. But we can connect it with a Micro B male to Standard A
>> male cable which is very easy to get:
> Yes, that may be an option. Anelok needs a Full A to Micro B cable
> anyway, so that combination may not be overly clumsy. As an added
> benefit, it also solves the problem of having a sufficiently long
> cable for power, since it's easy to get these cables in all kinds of
> lengths.
>> The second one has a chip inside.
> Oh, I didn't expect this. Are there any markings on the chip that
> could tell us what it does ?
>> It cannot work properly when all three ends are in use.
> Maybe the chip implements some of these fancy OTG protocols, e.g.,
> HNP (Host Negotiation Protocol) which lets a B device become host,
> just to get it wrong :)
>> Another cable Xiangfu ordered should arrive in a few days. I will
>> test it later.
> Great ! Let's see what this does.
> Thanks a lot ! This looks very good.
> - Werner
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The third one has arrived but to my disappointment, it is nothing but a 

And about the chip on the second one:
I searched for the name, FC18XZ 436GA, but got no result. Sound like a 
custom chip.
According to its instructions, this cable can be used in three modes:
- USB charging/SYNC mode: use full usb male and micro usb
- USB to USB extension mode: use full usb male and full usb female
- USB OTG mode: use full usb female and micro usb
When all three ports are in use, it is in USB charging/SYNC mode and 
ignores the device connected to full usb female.
I tried cutting off the two data wires on the full usb female side but 
that did not help either.

Anyway, the first Y-cable should be ok. We have ordered some more and 
will ship some to you.


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