[E3-hacking] About connecting to the serial on the E3

[David Given]

Provided the E3 and the USB device ran off isolated supplies, you might be
able to get away with connecting the 5V (or whatever) on the USB adapter to
the GND on the jack. That would cause the logic levels to be interpreted
inverted.

Note, this does not constitute advice, not responsible for any device
destruction caused by doing this, etc...

On Thu, 4 Apr 2019, 11:51 Sean Furey, <sean-lists-e3-hacking at furey.me.uk>
wrote:

> On Thu, Apr 04, 2019 at 08:19:35AM +0100, Brian Walton wrote:
> > If the E3 has a TTL serial port as reported here then a USB to TTL serial
> > adapter should work fine.
>
> I seem to remember the logic levels used by the E3 to be the reverse of
> what is normally used for TTL serial, hence the need for an invertor.
> Don't know if the USB TTL serial devices support that variation.
>
> When I briefly was playing with this a long time ago I used:
>
> - USB to RS232
> - MAX (of some sort) to level shift to TTL
> - MAX (well same one, it had two sets of level shifters) to level shift
> back to RS232
> - E3
>
> From what I remember, the MAX was liberal enough on the RS232 rx side
> attached to the E3 tx line to cope with the non-RS232 levels.  As for the
> E3 rx line, I presume it coped ok, but in hindsight I'm a little surprised.
>
> Sean
>
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