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I believe I can use the uP VBUS detect pin to detect the B
connector. Then its just a matter of finding a power switch that can
limit current on the A connector, and can be turned off of course.<br>
<br>
Thanks everyone!<br>
<br>
<br>
<div class="moz-cite-prefix">On 9/23/2015 10:23 AM, Vladimir
Pantelic wrote:<br>
</div>
<blockquote
cite="mid:CADBCB7Eh0gOXNCPHr6oBBtBgAXooeET9MJ8nyDmygMj9OHRDBw@mail.gmail.com"
type="cite">
<p dir="ltr">yes, that is doable</p>
<div class="gmail_quote">On Sep 23, 2015 7:08 PM, "Tim Ressel"
<<a moz-do-not-send="true"
href="mailto:timr@circuitabbey.com">timr@circuitabbey.com</a>>
wrote:<br type="attribution">
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">This will be
for USB Midi, so the host connector needs to be powered and
the device connector does not. But I should be able to sense
power on the device connector and switch accordingly? Default
to host and switch to device upon power on the device
connector?<br>
<br>
--TimR<br>
<br>
On 9/23/2015 9:56 AM, <a moz-do-not-send="true"
href="mailto:rsdio@audiobanshee.com" target="_blank">rsdio@audiobanshee.com</a>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
One correction to my comments: Whether your Device mode is
self-powered or not, you always need to be able to read the
power coming from the USB B connector to ensure that your
CPU does not enable or drive the data lines unless power is
present. That's one of the basic rules of USB. So, this
means that your source for USB power over the A connector
cannot connect to the power on the B connector, otherwise
you'll never know.<br>
<br>
The only thing missing from the EK-TM4C1294 LaunchPad is an
example circuit for a system with both A and B connectors,
so that's where we're getting into new territory. If anyone
knows of an evaluation board that does have both A and B -
especially with schematics freely available - then please
share with the list.<br>
<br>
B<br>
<br>
<br>
On Sep 23, 2015, at 9:47 AM, <a moz-do-not-send="true"
href="mailto:rsdio@audiobanshee.com" target="_blank">rsdio@audiobanshee.com</a>
wrote:<br>
On Sep 22, 2015, at 11:28 PM, Vladimir Pantelic <<a
moz-do-not-send="true" href="mailto:vladoman@gmail.com"
target="_blank"><a class="moz-txt-link-abbreviated" href="mailto:vladoman@gmail.com">vladoman@gmail.com</a></a>> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
On 23.09.2015 08:10, Tim Ressel wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
I need to design a usb interface that does both host and
device, but not<br>
at the same time. There will be an A and B connector on
the front<br>
panel. All of the procs I've looked at only have one
USB interface.<br>
I'm guessing the thing to do here is to use a USB
switch. Anyone have<br>
some insights?<br>
</blockquote>
many CPU'S have a so called USB-OTG (on the go) interface
that allows to<br>
switch roles between host and device.<br>
<br>
normally switching to host mode is done by inserting a
cable that has<br>
the ID pin (the 5th pin on a USB mini/micro connector)
grounded, but it<br>
can of course also be done under SW control.<br>
<br>
look at e.g. the STM32F105, it has a: "USB 2.0 full-speed<br>
device/host/OTG controller with on-chip PHY that supports
HNP/SRP/ID"<br>
</blockquote>
Check out the Texas Instruments EK-TM4C1294XL LaunchPad
(about US$20).<br>
<br>
It has an ARM Cortex-M4 with USB OTG and good source code
examples. They have examples of Host firmware and examples
of Device firmware. The documentation makes a big deal of
the fact that none of the examples will switch between Host
and Device for you, so I imagine the solution is to read the
OTG input pin and then "reboot" into the other mode when it
changes. It doesn't seem like it will be too difficult. I've
tested their USB Audio Class Host firmware example, and it
works fine. I assume that the USB Device firmware is even
simpler, and also functional.<br>
<br>
The EK-TM4C1294XL LaunchPad is also a good example of the
circuit needed. The technical manual for that LaunchPad has
the full schematic. One interesting component on the board
is a chip that controls the current being fed to the Host
port to power the external Device. You'll need to keep the
power on the A and B connectors separate. It will be
challenging if you want to power your board entirely from
USB when acting as a Device, and probably much easier if
your board is always self-powered. You'll need to be able to
read the B connector power on a 5-Volt-tolerant GPIO pin to
detect external power unless you're always self-powered. I
think that the ground and differential USB data can be
shared between the A and B.<br>
<br>
I'm sure there are other options, but I wanted to point out
that the TM4C1294 has good examples for the circuits and
source for the firmware.<br>
<br>
Brian Willoughby<br>
Sound Consulting<br>
<br>
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<br>
</blockquote>
<br>
-- <br>
--Tim Ressel<br>
Circuit Abbey<br>
<a moz-do-not-send="true" href="mailto:timr@circuitabbey.com"
target="_blank">timr@circuitabbey.com</a><br>
<br>
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</blockquote>
</div>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
--Tim Ressel
Circuit Abbey
<a class="moz-txt-link-abbreviated" href="mailto:timr@circuitabbey.com">timr@circuitabbey.com</a></pre>
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