no KL27; Y-cable news (was Re: Anelok: one more MCU - maybe an idea for later)

Werner Almesberger werner at almesberger.net
Sun Dec 28 18:46:41 UTC 2014


I wrote:
> KL27	32-QFN	256 kB	MKL27Z256VFM4	3.185

Oops, this one wouldn't do: the USB in KL27 (and relatives: KL17, KL43,
maybe more) is only device ("slave" as Freescale call it), not OTG.


Speaking of OTG, it seems that Y-cable research has made some important
breakthroughs since the last time I checked, and they have now caught
up with our needs. Here are a few cables that seem to be roughly
equivalent to the original Y-box:

- cheap, but cable is a bit short:
  http://www.dhgate.com/product/4in-10cm-micro-usb-male-to-usb-a-female-host/160586976.html

- a bit longer (19 + 30 cm):
  http://www.ebay.com/itm/HOT-Micro-USB-Male-To-USB-Female-Host-OTG-Cable-USB-Power-Cable-Y-Splitter-/251466791571

- here's one from a reputable brand. Alas, it seem that they're
  replacing this one with a model that has a Micro USB 3.0 connector:
  https://www.lacie.com/au/products/product.htm?id=10575

- one more, this time from eBay:
  http://www.ebay.com/itm/2014-Hot-Micro-USB-Male-To-USB-Female-Host-OTG-Cable-USB-Power-Cable-Y-Splitt-/131178750551

  Interesting detail: "does not support OTG phone or tablet charging".
  Hmm. VBUS not connected between USB A male and Micro B male ? That
  would suck.

  But then, they have some other peculiar ideas: "the disk must be
  formatted as FAT32." Must be one heck of a smart cable ! :)

- also available with angled Micro B:
  http://www.ebay.com/itm/New-Micro-USB-Male-To-USB-Female-Host-OTG-Cable-USB-Adapter-Cable-Y-Splitter-/331424502420

Anyone care to get one of these critters and measure how it's
connected on the inside ?

It's interesting that they all are Micro B not Micro A. I wonder what
they do with the ID pin. But if the industry chooses to ignore AB and
just uses B for both roles, then I'll be the last to complain: while
the shield of a Micro B receptacle will reliably stop a reversed plug,
Micro AB - and I guess also Micro A - relies on a fragile-looking piece
of plastic for this.

Availability of Y-cables also means that developing the Y-box is less
important and we may end up not needing it at all.

- Werner



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