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Re: [gpsd-dev] Very basic PPS question:

From: Gary E. Miller
Subject: Re: [gpsd-dev] Very basic PPS question:
Date: Mon, 21 Oct 2013 11:48:35 -0700

Yo Hal!

On Sat, 19 Oct 2013 13:19:19 -0700
Hal Murray <address@hidden> wrote:

> address@hidden said:
> > I am not an expert.  I have heard that it can go either way, it can
> > be device-dependent, and there is a window around the PPS edge
> > (which can be the leading or trailing edge) where NTP will
> > "associate" the NMEA sentence with the PPS signal.  The window can
> > be fudged to be earlier or later than its default position. 
> All the device manufacturers that I'm familiar with use the
> leading/rising edge of the PPS pulse.

We have seen 1HZ square waves which is the 'leading' edge?  We have also
seen 0.5Hz suqare waves where each edge is used.

> The confusion comes when people connect it to a modem control pin
> rather than a normal TTL/CMOS level logic receiver.  Almost all the
> TTL/CMOS to RS-232 converter chips include an inverter

Yes, that too.

> So does the kernel interface.

KPPS reports both edges and leaves it to the client to decide what edge
is important.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
        address@hidden  Tel:+1(541)382-8588

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