[time-nuts] Serial port splitter s/w

Hal Murray hmurray at megapathdsl.net
Wed Feb 26 13:30:58 EST 2014


david.partridge at perdrix.co.uk said:
> I looked around the with Google, and saw *numerous" serial port splitters.
> Which is recommended?

If your lines are short, you don't need fancy hardware.  The RS-232 driver 
will drive 2 lines.  Just take 2 cables, cut them in half, connect the 
wires...

> Also what's the best way how to configure NTP to lock the the TB on a serial
> port?  Do I need to modify the TB to deliver the PPS down one of the serial
> data lines or will NTP work well by parsing the NMEA time messages? 

Yes, you need to connect the PPS.  You can get the PPS by just opening up the 
TB and soldering a wire from the BNC to the DB-9.

You may/probably need a pulse stretcher.  I have one TB where I changed the 
PPS wire to a diode and R/C.  It's a kludge, but works.  You can get a clean 
version from TAPR.  It needs power.
  http://tapr.org/kits_fatpps.html

TBs don't talk NMEA.  Use the Palisade driver.

The problem is that both LH and ntpd expect to talk to the TB.  It may work 
if you let one of them listen to whatever traffic the other one generates.  
ntpd just sets it up so a couple of packet types get sent every second.  If 
LH does something similar, it should work.  (I think ntpd will ignore 
everything else.  It it complains too loudly we can fix it.)


-- 
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