On Mon, Nov 11, 2013 at 2:10 AM, Christopher Havel
<laserhawk64@gmail.com> wrote:

On 11/10/2013 9:08 PM, luke.leighton wrote:

apologies to everyone on the list - you may have noticed i'm using
brief and curt language at the moment.  it's not personal: i just have
far less time available and have to be very focussed.
l.

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Sorry to hear you're so busy. Can I help? :D

 yes.  i thought of something.
http://permalink.gmane.org/gmane.comp.hardware.netbook.arm/7597

 could you investigate, find some "educational" style electronics
explanations online, as to why henrik's recommendation to use a
pull-up resistor to 3.3V and a reversed-diode between the Tx UART and
incoming Rx actually works?  i'm attaching a small diagram showing the
circuit.

 it can then be added here:
http://elinux.org/Embedded_Open_Modular_Architecture/EOMA-68#Requirements_for_UART

 also i think.... to avoid too big a voltage-drop it should be a zener
diode otherwise it might interfere with the thresholds.

  basically i think the way it works is that 0 logic level on UART is
"positive voltage", and the Tx line "sucks" current down to GND in
order to indicate a "1".  therefore, normally (i.e. without the diode)
current would be flowing *from* Rx *to* Tx if Tx is held at GND to
indicate a "1"... so putting the diode in the circuit is... well...
normal!

l.

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