On 17/07/2020 14:07, R.Wieser wrote:
> Alister,
>
>> Tx & RX are described as TTL serial TTL is a
>> fully detailed standard as far as signal levels go.
>
> Your second mistake.
>
> Just take a look here:
>
> https://www.sparkfun.com/tutorials/215
>
> "Serial communication at a TTL level will always remain between the limits
> of 0V and Vcc, which is often 5V or 3.3V"
>
> Nowerdays a "TTL signal" often doesn't refer to the voltage, but to the
> "low"/"zero" level being at 0v, and the "high"/"one" level being at VCC
> (regardles of what VCC might be) - as opposed to an RS232 specced signal,
> where "low" is at +v and "zero" at -v.
>
>
> And I see that you did not read my initial message too closely.   In it I
> wrote that the RXD and TXD pins are specced as having 3.3v levels ...
>
> Regards,
> Rudy Wieser
>
>
FWIW there is somewhere the original TTL spec where 0 is less than some
voltage and 1 is more than some voltage with in between being 'here be
dragons'

"A TTL input signal is defined as "low" when between 0 V and 0.8 V with
respect to the ground terminal, and "high" when between 2 V and VCC (5 V)"

Whether or not what you are discussing conforms to that, I do not know.
Just my 2 pennoth..

--
“It is dangerous to be right in matters on which the established
authorities are wrong.”

― Voltaire, The Age of Louis XIV

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