[ntp:questions] Re: Meaning of PPS flag2 -- assert/clear

Hal Murray hmurray at suespammers.org
Sat Oct 7 04:07:35 UTC 2006


>Can someone tell me definitively the electrical meaning of pps driver
>flag2?  More precisely, how should flag2 be set for:
>
>1.  Signal on DCD line normally high, going low at the on-time mark
>
>2.  Signal on DCD line normally low, going high at the on-time mark

RS-232 is upside down, so "assert" means low.

So the normal case triggers on a falling edge and the
"flag2 1" case triggers on the rising edge.



>In each case, it's the initial transition that's on-time; the trailing
>edge of the pulse is not precise.

Years ago, my Z3801A was off a few 10s of uSec relative to a NMEA
receiver.  The pulse is 20 uSec wide.  Things got happier after I added
the "flag2 1" to my config file.

It's possible my mods to the Z3801A are different from what others
are using.  I'm pretty sure I copied Jeff Mock's drections, but of
course I made a few "improvements".  I think they were all physical
rather than logical.

On a scope, my pulse is normally low, going high for 20 uSec.
(I'm actually standing on my head because the easy place to get
a scope probe is before a RS-232 driver.  So I could easily have
something inverted.)

Looks like my comment in
  http://ntp.isc.org/bin/view/Support/ConfiguringHPZ3801ARefclocks
is backwards/confusing.  Sigh.

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