[time-nuts] RS 232

Tim Shoppa tshoppa at gmail.com
Thu Jul 25 11:58:31 EDT 2013


A lot of these questions can be side-stepped today because few to no modern
PC's have built in RS-232 serial ports.

And if you are going to add a serial port you can just put in a RS-422 PCI
card or RS-422 to USB interface instead. A big win, and it makes much more
sense to leach +5V off of USB than it does to leach power off RS-232
control lines.

Many time-nut devices are already RS-422 (e.g. Z3801A) serial and
differential for PPS, and it makes little sense today to backhaul to RS-232
when a new PC won't have native RS-232 support anyway.

Tim N3QE


On Thu, Jul 25, 2013 at 9:39 AM, <EWKehren at aol.com> wrote:

> Since joining time nuts over four years ago I have not used a  single MAX
> 232 chip. Two reasons MAX do not give me isolation and do generate  noise
> in
> critical applications. I prefer the use of two H11 opto couplers which
>  work
> perfect. On the receiving end the diode along with a current limiter and
> blocking diode for the negative level works perfect. On the output side a
> power  source is needed. If one uses an USB adapter it does have the + 5
> volt
> which  again works perfect.  How ever many prefer to use RS 232 direct and
> that is  why I hope to get some comments and suggestions from the list.
> Corby
> used on our  counter circuit that he described a separate power source.
> Present MAX circuits use a + 1.4 volt threshold but  considering legacy the
> question is what should the voltage swing be to make it  compatible for
> most PC's and what options exist to get the necessary voltage. In  the past
> other pins on the RS 232 port where an ideal power source. Still an
>  option?
> Bert Kehren
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