On 4/1/2016 10:28 PM, Pavel Shatov wrote:
On 01.04.2016 19:57, Jacob wrote:
What's the purpose of J2/J3?
Jacob
Sorry, forgot to answer this one.
We currently have two USB-to-UART transceivers by FTDI onboard. There
was a heated discussion on the list (FTDI is notorious for their driver
issues, etc), I'm not going to reproduce all the details, but it all
boiled down to the fact, that we eventually decided to try replacing
them with some small general-purpose USB-capable ARM processor.
We decided to add these headers, so that this custom transceiver could
be designed independently. They will enable us to unsolder the FTDIs and
test the transceiver with Alpha board. If it works out with Alpha, we'll
use it for Alpha2 or Beta board instead of FTDIs.
So if those headers are for a dev option and not for the end-user, I'd
recommend to change them to 0 Ohm resistors (preferably 0402 or, if you
wish for ease of "basement soldering", 0603).
The reason is that USB signalling requires special care - differential
routing with controlled impedance and away from other noisy lines - and
the big header pads break that path.
If you leave it as it is now, the USB interface will still work, albeit
at reduced speed due to re-negotiation of lost packets.
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