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Re: [gpsd-dev] Very basic PPS question:
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From: |
Gary E. Miller |
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Subject: |
Re: [gpsd-dev] Very basic PPS question: |
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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.
RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
address@hidden Tel:+1(541)382-8588
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