"unruh" <[email protected]> wrote in message
news:[email protected]...
[]
For timing it is only the rise time that is important. The length of the
pulse is irrelevant, unless your Hardware/software requires a given
length pulse in order to recognize and interrupt ( and if it did , it
would be broken since it had better interrupt on the rising edge if it
is to be useful to timing. )
Certainly if you are using TTl-RS232 converters their times are
important. However most rs232 cards will handle ttl signals fine anyway.
Distinguish, though, between internal-level signals where a 100 ns pulse
may be quite enough, and signals sent down cables where the pulse length
needs to be sufficient to allow the signal to be recognised at the other
end. I've seen RS-232 inputs with quite strong filtering, and taking
115,200 baud as a typical maximum for older units, I would not want a
pulse less than 10 microseconds long. First guess estimate.
How well the rise-time needs to be preserved depends on the precision
required - I would take more care where sub-microsecond precision was
needed.
The 100 ms pulse from the GPS 18/x and the Sure board is nice because you
can put an LED (or scope) on that line and see the pulse, giving visual
confirmation of PPS data.
Cheers,
David
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