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

John Ackermann N8UR jra at febo.com
Sat Oct 7 13:43:27 UTC 2006

Hal Murray said the following on 10/07/2006 12:07 AM:

> 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.)

On my Z3801A, with this part of the mod done per Jeff's page and
measuring the signal on the RS-232 wire using a breakout box, the DCD
line is normally high and goes low for 20us; that's what I would
consider "normal" RS-232 behavior, though most PPS sources are just the
opposite since they're using a positive going pulse.

By the way, I have my own mods page for the Z3801A at


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

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