[Arm-netbook] [EOMA68] RS232 on SoCs

[luke.leighton]

On Sat, Aug 31, 2013 at 3:23 PM, Ryan Mullen <rmmullen at gmail.com> wrote:
> Hi Luke,
>
> Sorry, just to clear up my confusion - at what point does RS232 come
> into play here? I was under the impression that the UART lines on the
> EOMA connector were TTL,

 the *standard* says they have to be TTL, and tri-state (floating) on
start-up.  i'd assumed that the A20 CPU's GPIO lines were
TTL-compliant and also tristate *especially* when power is not
applied...

 ... henrik's pointed out that that's *not* the case.

> I'm not sure I understand why connecting, say, 5V to the UART RX line
> with the A20 powered off would cause any problems (unless there is an
> excessive current situation). I typically work with lower end micros
> and I've never worried about it before...

 yeah - don't know the answer, but it does need to be resolved.

l.