[Arm-netbook] apologies

[joem]

On Tue, 2013-11-12 at 12:09 +0000, luke.leighton wrote:
> On Mon, Nov 11, 2013 at 2:10 AM, Christopher Havel
> <laserhawk64 at 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.
> >>
> >> _______________________________________________
> >> arm-netbook mailing list arm-netbook at lists.phcomp.co.uk
> >> http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook
> >> Send large attachments to arm-netbook at files.phcomp.co.uk
> >
> > 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.

Henrik's idea should work - the diode should be a schottky diode with
0.2V to 0.3V drop as hinted in the drawing otherwise a 0.7V drop with a
normal diode may be too high to allow a logic 0 to be registered.

The down side of the circuit is that the pull up resistor needs to be
connected to the 3.3V line, which is inside the EOMA and not accessible.

Also - if higher baud rates don't work try decreasing the value of the
resistor.