Yes, you're right, that's clearly nonsense.

Why would the E3 generate an inverted signal, anyway? If it's just the raw output from the processor (which I think it is) then it should be standard TTL levels, because it's supposed to be fed into something like a MAX232 for conversion to RS232 levels. Inverting it but leaving it at TTL seems very odd.

On Thu, 4 Apr 2019, 14:25 Sean Furey, <sean-lists-e3-hacking@furey.me.uk> wrote:

On Thu, Apr 04, 2019 at 12:18:56PM +0200, David Given wrote:
> 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.

I'd have thought that would make the USB dev see the E3's 0V - 5V as 5V - 10V, and the E3 to see the USB's 0V - 5V as -5V - 0V. Which doesn't sound like it helps - am I missing something?

Sean

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