[ntp:questions] Re: Meaning of PPS flag2 -- assert/clear
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
Looks like my comment in
is backwards/confusing. Sigh.
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