[Gllug] serial trigger level

[Chris Bell]

On Wed 03 Dec, Peter Childs wrote:
> 
> Chris Bell wrote:
> 
>
> >>
> >   Are you having problems caused by different earths, or low signal levels?
> >You could try a ferrite common mode filter that clips round the cable, or a
> >few turns through a larger ferrite core (I use the core from an old TV line
> >output transformer), otherwise optical isolators or pulse transformers.
> >
> >  
> >
>     Its not garbled messages as that would produce its sending. Its 
> missing characters. The error can be recreated with a python script and 
> a loop back cable.  :)
>     Yes setserial should be the right command but it seams to be a 
> missing feature.  Current theory is I can reporgram the uart with a one 
> line C program. So I might have to patch setserial and give the patch to 
> the right developer... (Grone..)
> 
> Peter Childs
> 
> 
   Random variations in low level interference would cause that, so if you
think that changing the trigger level might help you should also consider
the other possibilities.
   Standard logic chips work between 0v and +5v supplies, and require input
levels to switch either side of a prohibited range which will depend on the
chip type. Their outputs are capable of ensuring that this happens with a
safe margin.
   Interface chips are usually designed to output larger than normal
signals, and be reasonably tolerant of input levels, so as to be fairly
reliable over difficult links.
   Standard RS232 drivers can use +/- 15v supplies generated within the chip
using diode pump circuits. Unfortunately serial connections tend to be used
over long distances where there can be damage caused by earth currents or
lightning.

-- 
Chris Bell


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