[Arm-netbook] [EOMA68] RS232 on SoCs

[luke.leighton]

On Sat, Aug 31, 2013 at 2:16 PM, Henrik Nordström
<henrik at henriknordstrom.net> wrote:

> Yes, once the SoC is powered then there is no problem to connect 3.3V to
> the RX pin. But it is generally not OK to provide power to an SoC I/O
> pin with the I/O bank powered off.

 ... ah.  right.

 so, really, this should be noted in the EOMA68 specification, because
i've added UART (not just for convenience but because it's needed for
debugging as well as for programming / booting things like the STM32F
on the flying squirrel).

so, really, hmmm... *ponders*.... actually this EOMA68-A20 CPU Card
breaks the specification: the pins should be tri-state (floating).  i
didn't realise the A20 would... arg ok.

so what's best here?  if supporting the ability to use the pins for
other purposes (even if it's not part of the spec) they have to be
"direct". which means putting the buffering on the I/O board side.

however if protecting dash molly-coddling people it means putting a
buffer on the CPU Card.

... thoughts?

l.